diff --git a/epicinium/src/ai/ai.cpp b/epicinium/src/ai/ai.cpp
index 5765a54..45d2969 100644
--- a/epicinium/src/ai/ai.cpp
+++ b/epicinium/src/ai/ai.cpp
@@ -131,3 +131,13 @@ const std::vector<std::string>& AI::hiddenPool()
 	};
 	return pool;
 }
+
+const std::vector<std::string>& AI::selfHostedPool()
+{
+	static std::vector<std::string> pool = {
+		"RampantRhino",
+		"HungryHippo",
+		"ChargingCheetah",
+	};
+	return pool;
+}
diff --git a/epicinium/src/ai/ai.hpp b/epicinium/src/ai/ai.hpp
index 2b7ff6a..1fe9989 100644
--- a/epicinium/src/ai/ai.hpp
+++ b/epicinium/src/ai/ai.hpp
@@ -45,6 +45,7 @@ class AI
 	static std::string libraryDefaultFilename(const std::string& name);
 
 	static const std::vector<std::string>& pool();
+    static const std::vector<std::string>& selfHostedPool();
 
 private:
 	static const std::vector<std::string>& hiddenPool();
diff --git a/epicinium/src/ai/aichallenge.cpp b/epicinium/src/ai/aichallenge.cpp
index 699df53..366dd35 100644
--- a/epicinium/src/ai/aichallenge.cpp
+++ b/epicinium/src/ai/aichallenge.cpp
@@ -37,21 +37,14 @@ const char* AIChallenge::getKey(const Challenge::Id& id)
 	switch (id)
 	{
 		case CUSTOM: return "";
-		// OLD: "showcase_2018_07_04";
-		// OLD: "elimination_2017_07_20";
-		// OLD: "everythingisfree_2018_07_16";
 		// OLD: "trample_2017_08_01";
-		// OLD: "trample_2018_11_26";
-		// OLD: "highspeed_2018_09_21";
-		// OLD: "investment_2019_04_15";
-		// OLD: "morale_2020_05_06";
-		case SHOWCASE: return "showcase_2021_05_25";
-		case ELIMINATION: return "elimination_2021_05_25";
-		case EVERYTHINGISFREE: return "everythingisfree_2021_05_25";
-		case TRAMPLE: return "trample_2021_05_25";
-		case HIGHSPEED: return "highspeed_2021_05_25";
-		case INVESTMENT: return "investment_2021_05_25";
-		case MORALE: return "morale_2021_05_25";
+		case SHOWCASE: return "showcase_2018_07_04";
+		case ELIMINATION: return "elimination_2017_07_20";
+		case EVERYTHINGISFREE: return "everythingisfree_2018_07_16";
+		case TRAMPLE: return "trample_2018_11_26";
+		case HIGHSPEED: return "highspeed_2018_09_21";
+		case INVESTMENT: return "investment_2019_04_15";
+		case MORALE: return "morale_2020_05_06";
 	}
 	return "";
 }
@@ -165,7 +158,7 @@ const char* AIChallenge::getRulesetName(const Challenge::Id& id)
 {
 	switch (id)
 	{
-		case CUSTOM: return "";
+		case CUSTOM: return "challenge_custom";
 		case SHOWCASE: return "";
 		case ELIMINATION: return "";
 		case EVERYTHINGISFREE: return "challenge_everythingisfree";
diff --git a/epicinium/src/ai/aineuralnewt.cpp b/epicinium/src/ai/aineuralnewt.cpp
index 8df70cb..d4c8aee 100644
--- a/epicinium/src/ai/aineuralnewt.cpp
+++ b/epicinium/src/ai/aineuralnewt.cpp
@@ -28,6 +28,9 @@
 #include "aim.hpp"
 #include "bible.hpp"
 
+ // windows.h is being annoying
+#undef near
+
 
 std::string AINeuralNewt::ainame() const
 {
@@ -937,7 +940,10 @@ void AINeuralNewt::moveDefense(const Descriptor& unitdesc,
 	for (Cell at : _board)
 	{
 		if (_board.gas(at)) continue;
-		if (_board.frostbite(at)) continue;
+		if (_board.frostbite(at)
+			// In Spring, frostbite is used to indicate "Chilled" units.
+			&& !(_bible.frostbiteGivesColdFeet()
+				&& _bible.chaosMinFrostbite(_season) < 0)) continue;
 		if (_board.firestorm(at)) continue;
 		if (_board.death(at)) continue;
 		int threatdis = _enemyBaseFloodfill.steps(at);
diff --git a/epicinium/src/ai/airampantrhino.cpp b/epicinium/src/ai/airampantrhino.cpp
index eb6d7e8..1839641 100644
--- a/epicinium/src/ai/airampantrhino.cpp
+++ b/epicinium/src/ai/airampantrhino.cpp
@@ -29,6 +29,9 @@
 #include "aim.hpp"
 #include "bible.hpp"
 
+ // windows.h is being annoying
+#undef near
+
 
 std::string AIRampantRhino::ainame() const
 {
@@ -1530,6 +1533,14 @@ bool AIRampantRhino::checkLockdown(const Descriptor& unitdesc)
 {
 	Cell at = _board.cell(unitdesc.position);
 
+	bool canUseAbilities = true;
+	if (_bible.frostbiteGivesColdFeet()
+		// In Spring, frostbite is used to indicate "Chilled" units.
+		&& _board.frostbite(at) && _bible.chaosMinFrostbite(_season) < 0)
+	{
+		canUseAbilities = false;
+	}
+
 	std::vector<Move> dirs = {Move::E, Move::S, Move::W, Move::N};
 	std::random_shuffle(dirs.begin(), dirs.end());
 	for (const Move& move : dirs)
@@ -1540,7 +1551,7 @@ bool AIRampantRhino::checkLockdown(const Descriptor& unitdesc)
 		if (_board.ground(target)
 			&& _board.ground(target).owner != _player)
 		{
-			if (canUseCombatAbilities())
+			if (canUseAbilities && canUseCombatAbilities())
 			{
 				UnitType unittype = _board.ground(at).type;
 				std::vector<Bible::TileBuild> shapes = _bible.unitShapes(
@@ -1567,6 +1578,7 @@ bool AIRampantRhino::checkLockdown(const Descriptor& unitdesc)
 						Descriptor::cell(target.pos()));
 				}
 			}
+
 			return true;
 		}
 	}
@@ -1588,6 +1600,13 @@ void AIRampantRhino::controlIdleDefense(const Descriptor& unitdesc)
 
 	Cell at = _board.cell(unitdesc.position);
 
+	if (_bible.frostbiteGivesColdFeet()
+		// In Spring, frostbite is used to indicate "Chilled" units.
+		&& _board.frostbite(at) && _bible.chaosMinFrostbite(_season) < 0)
+	{
+		return;
+	}
+
 	std::vector<Move> dirs = {Move::E, Move::S, Move::W, Move::N};
 	std::random_shuffle(dirs.begin(), dirs.end());
 	for (const Move& move : dirs)
@@ -1613,6 +1632,13 @@ void AIRampantRhino::controlCaptor(const Descriptor& unitdesc)
 {
 	Cell at = _board.cell(unitdesc.position);
 
+	if (_bible.frostbiteGivesColdFeet()
+		// In Spring, frostbite is used to indicate "Chilled" units.
+		&& _board.frostbite(at) && _bible.chaosMinFrostbite(_season) < 0)
+	{
+		return;
+	}
+
 	if (_board.tile(at)
 		&& _board.tile(at).owner != _player
 		&& _bible.tileOwnable(_board.tile(at).type))
@@ -1643,7 +1669,10 @@ void AIRampantRhino::controlBlocker(const Descriptor& unitdesc)
 		if (at == from) continue;
 		if (_board.ground(at)) continue;
 		if (_board.gas(at)) continue;
-		if (_board.frostbite(at)) continue;
+		if (_board.frostbite(at)
+			// In Spring, frostbite is used to indicate "Chilled" units.
+			&& !(_bible.frostbiteGivesColdFeet()
+				&& _bible.chaosMinFrostbite(_season) < 0)) continue;
 		if (_board.firestorm(at)) continue;
 		if (_board.death(at)) continue;
 		if (isTarget(at.pos())) continue;
@@ -1758,7 +1787,10 @@ void AIRampantRhino::controlDefense(const Descriptor& unitdesc)
 		if (at != from && _board.ground(at)
 				&& _board.ground(at).owner == _player) continue;
 		if (_board.gas(at)) continue;
-		if (_board.frostbite(at)) continue;
+		if (_board.frostbite(at)
+			// In Spring, frostbite is used to indicate "Chilled" units.
+			&& !(_bible.frostbiteGivesColdFeet()
+				&& _bible.chaosMinFrostbite(_season) < 0)) continue;
 		if (_board.firestorm(at)) continue;
 		if (_board.death(at)) continue;
 		if (isTarget(at.pos())) continue;
@@ -1911,7 +1943,10 @@ void AIRampantRhino::declareOffense(const Descriptor& unitdesc)
 		if (at != from && _board.ground(at)
 				&& _board.ground(at).owner == _player) continue;
 		if (_board.gas(at)) continue;
-		if (_board.frostbite(at)) continue;
+		if (_board.frostbite(at)
+			// In Spring, frostbite is used to indicate "Chilled" units.
+			&& !(_bible.frostbiteGivesColdFeet()
+				&& _bible.chaosMinFrostbite(_season) < 0)) continue;
 		if (_board.firestorm(at)) continue;
 		if (_board.death(at)) continue;
 		if (isTarget(at.pos())) continue;
@@ -2055,6 +2090,13 @@ void AIRampantRhino::controlBombarder(const Descriptor& unitdesc)
 	Cell from = _board.cell(unitdesc.position);
 	const UnitToken& unit = _board.ground(from);
 
+	if (_bible.frostbiteGivesColdFeet()
+		// In Spring, frostbite is used to indicate "Chilled" units.
+		&& _board.frostbite(from) && _bible.chaosMinFrostbite(_season) < 0)
+	{
+		return;
+	}
+
 	UnitType unittype = unit.type;
 	int rangeMin = _bible.unitRangeMin(unittype);
 	int rangeMax = _bible.unitRangeMax(unittype);
diff --git a/epicinium/src/common/header.hpp b/epicinium/src/common/header.hpp
index f38fe62..bda70ff 100644
--- a/epicinium/src/common/header.hpp
+++ b/epicinium/src/common/header.hpp
@@ -149,3 +149,7 @@ struct stringref;
 #ifndef EDITOR_DEPRECATED_ENABLED
 #define EDITOR_DEPRECATED_ENABLED false
 #endif
+
+#ifndef NEURALNEWT_20x13_ENABLED
+#define NEURALNEWT_20x13_ENABLED false
+#endif
diff --git a/epicinium/src/common/locator.cpp b/epicinium/src/common/locator.cpp
index 3366e29..eb5edac 100644
--- a/epicinium/src/common/locator.cpp
+++ b/epicinium/src/common/locator.cpp
@@ -30,6 +30,7 @@
 std::string Locator::_resourceroot = "";
 std::string Locator::_cacheroot = "";
 std::string Locator::_authoredroot = "";
+std::vector<Locator::ExternalFolder> Locator::_externalfolders = {};
 
 void Locator::setResourceRoot(const std::string& root)
 {
@@ -119,6 +120,36 @@ std::string Locator::picture(const std::string& picturename)
 
 std::string Locator::pictureFilename(const std::string& picturename)
 {
+	if (picturename.find_first_of('@') != std::string::npos)
+	{
+		size_t seppos = picturename.find_first_of('/');
+		std::string shortname;
+		// Use x.rfind(y, 0) == 0 as x.starts_with(y).
+		if (picturename.rfind("panels/", 0) == 0)
+		{
+			shortname = "panel";
+		}
+
+		if (!shortname.empty() && seppos != std::string::npos)
+		{
+			std::string tag = picturename.substr(seppos + 1);
+			for (const auto& folder : _externalfolders)
+			{
+				if (folder.uniqueTag == tag)
+				{
+					return folder.sourcePath + shortname + ".png";
+				}
+			}
+			LOGW << "Failed to find external tag '" << tag << "'"
+				" for picture '" << picturename << "'";
+		}
+		else
+		{
+			LOGW << "Failed to determine shortname"
+				" for picture '" << picturename << "'";
+		}
+	}
+
 	return _cacheroot + "pictures/" + picturename + ".png";
 }
 
@@ -137,6 +168,20 @@ std::string Locator::pictureName(const std::string& fullfilename)
 
 std::string Locator::rulesetFilename(const std::string& rulesetname)
 {
+	if (rulesetname.find_first_of('@') != std::string::npos)
+	{
+		std::string tag = rulesetname;
+		for (const auto& folder : _externalfolders)
+		{
+			if (folder.uniqueTag == tag)
+			{
+				return folder.sourcePath + "ruleset.json";
+			}
+		}
+		size_t seppos = rulesetname.find_first_of('@');
+		std::string subpath = rulesetname.substr(seppos + 1);
+		return _cacheroot + "rulesets/external/" + subpath + ".json";
+	}
 	return _cacheroot + "rulesets/" + rulesetname + ".json";
 }
 
@@ -180,3 +225,58 @@ std::string Locator::fzmodelName(const std::string& fullfilename)
 	}
 	return "";
 }
+
+void Locator::useExternalFolder(ExternalFolder&& newFolder)
+{
+	LOGD << "Using '" << newFolder.uniqueTag << "'"
+		": " << newFolder.sourcePath;
+
+	for (auto& folder : _externalfolders)
+	{
+		if (folder.uniqueTag == newFolder.uniqueTag)
+		{
+			folder = newFolder;
+			return;
+		}
+	}
+
+	_externalfolders.emplace_back(newFolder);
+}
+
+void Locator::forgetExternalFolder(const std::string& uniqueTag)
+{
+	LOGD << "Forgetting '" << uniqueTag << "'";
+	_externalfolders.erase(
+		std::remove_if(
+			_externalfolders.begin(),
+			_externalfolders.end(),
+			[&](const ExternalFolder& folder) {
+				return folder.uniqueTag == uniqueTag;
+			}),
+		_externalfolders.end());
+}
+
+std::vector<std::string> Locator::externalRulesets()
+{
+	std::vector<std::string> rulesets;
+	for (const auto& folder : _externalfolders)
+	{
+		if (System::isFile(folder.sourcePath + "ruleset.json"))
+		{
+			rulesets.emplace_back(folder.uniqueTag);
+		}
+	}
+	return rulesets;
+}
+
+const std::vector<Locator::ExternalFolder>& Locator::externalFolders()
+{
+	return _externalfolders;
+}
+
+std::vector<std::string> Locator::listAuthoredRulesets()
+{
+	auto list = System::listDirectory(_authoredroot + "rulesets/", ".json");
+	std::sort(list.begin(), list.end());
+	return list;
+}
diff --git a/epicinium/src/common/locator.hpp b/epicinium/src/common/locator.hpp
index 299058e..df24146 100644
--- a/epicinium/src/common/locator.hpp
+++ b/epicinium/src/common/locator.hpp
@@ -28,6 +28,12 @@
 class Locator
 {
 public:
+	struct ExternalFolder
+	{
+		std::string uniqueTag;
+		std::string sourcePath;
+	};
+
 	static std::string picture(const std::string& picturename);
 
 	static std::string pictureFilename(const std::string& picturename);
@@ -45,9 +51,18 @@ class Locator
 	static std::string _resourceroot;
 	static std::string _cacheroot;
 	static std::string _authoredroot;
+	static std::vector<ExternalFolder> _externalfolders;
 
 public:
 	static void setResourceRoot(const std::string& root);
 	static void setCacheRoot(const std::string& root);
 	static void setAuthoredRoot(const std::string& root);
+
+	static void useExternalFolder(ExternalFolder&& folder);
+	static void forgetExternalFolder(const std::string& uniqueTag);
+
+	static std::vector<std::string> externalRulesets();
+	static const std::vector<ExternalFolder>& externalFolders();
+
+	static std::vector<std::string> listAuthoredRulesets();
 };
diff --git a/epicinium/src/common/system.cpp b/epicinium/src/common/system.cpp
index 980c5bc..cb0ea29 100644
--- a/epicinium/src/common/system.cpp
+++ b/epicinium/src/common/system.cpp
@@ -52,6 +52,10 @@ std::vector<std::string> System::listDirectory(const std::string& dirname,
 	}
 
 	std::vector<std::string> filenames;
+	if (!System::isDirectory(dirname))
+	{
+		return filenames;
+	}
 	for(const auto& p : fs::directory_iterator(dirname))
 	{
 		if (p.path().extension() == extensionPattern)
diff --git a/epicinium/src/common/writer.cpp b/epicinium/src/common/writer.cpp
index 6243eb7..5f72c4b 100644
--- a/epicinium/src/common/writer.cpp
+++ b/epicinium/src/common/writer.cpp
@@ -34,7 +34,7 @@
 
 
 static std::map<std::thread::id, Writer*> _installed;
-static std::mutex _mutex;
+static std::mutex _writerMutex;
 
 std::string Writer::write(const Json::Value& json)
 {
@@ -62,7 +62,7 @@ Writer::Writer()
 
 void Writer::install()
 {
-	std::lock_guard<std::mutex> lock(_mutex);
+	std::lock_guard<std::mutex> lock(_writerMutex);
 	_installed[std::this_thread::get_id()] = this;
 }
 
diff --git a/epicinium/src/logic/automaton.cpp b/epicinium/src/logic/automaton.cpp
index 8904a87..5952994 100644
--- a/epicinium/src/logic/automaton.cpp
+++ b/epicinium/src/logic/automaton.cpp
@@ -1298,6 +1298,10 @@ void Automaton::processMove(const Player& player, Order& order)
 	bool air = _bible.unitAir(movingunit.type);
 	bool gliding = false;
 
+	// When a unit has Cold Feet, they cannot attack until after they have
+	// moved. We check whether they currently have Cold Feet.
+	bool coldfeet = hasColdFeet(current);
+
 	// Before actually moving, we will determine how far we walk and if we will attack an enemy.
 	int moves = 0;
 	int attack = 0;
@@ -1418,6 +1422,7 @@ void Automaton::processMove(const Player& player, Order& order)
 
 			// Only some units can attack.
 			if (!_bible.unitCanAttack(movingunit.type)) break;
+			if (coldfeet) break;
 
 			// We can only attack if we can stop, or if we do a "bypass attack";
 			// in the latter case we can only have bypassed a single unit.
@@ -1628,6 +1633,13 @@ void Automaton::processGuard(const Player& player, Order& order)
 		return discarded(player, order, cset, Notice::ORDERINVALID);
 	}
 
+	// Does the unit get cold feet?
+	if (hasColdFeet(from))
+	{
+		LOGV << "unit has cold feet, order discarded";
+		return discarded(player, order, cset, Notice::COLDFEET);
+	}
+
 	// If the cell is empty, we cannot attack.
 	// If the unit is friendly, we cannot attack.
 	if (!otherunit || otherunit.owner == guardingunit.owner)
@@ -1716,6 +1728,13 @@ void Automaton::processFocus(const Player& player, Order& order)
 		return discarded(player, order, cset, Notice::ORDERINVALID);
 	}
 
+	// Does the unit get cold feet?
+	if (hasColdFeet(from))
+	{
+		LOGV << "unit has cold feet, order discarded";
+		return discarded(player, order, cset, Notice::COLDFEET);
+	}
+
 	// If the cell is empty, we cannot attack.
 	// If the unit is friendly, we cannot attack.
 	if (!otherunit || otherunit.owner == focussingunit.owner)
@@ -1811,9 +1830,6 @@ void Automaton::processLockdown(const Player& player, Order& order)
 		return discarded(player, order, cset, Notice::ORDERINVALID);
 	}
 
-	// This unit is now in lockdown mode.
-	_lockdowns.emplace_back(activeunit.id(), from, to);
-
 	// Before attacking, we look for a target.
 	const UnitToken& otherunit = _board.unit(to, desctype);
 	const TileToken& tile = _board.tile(to);
@@ -1826,6 +1842,16 @@ void Automaton::processLockdown(const Player& player, Order& order)
 		return discarded(player, order, cset, Notice::ORDERINVALID);
 	}
 
+	// Does the unit get cold feet?
+	if (hasColdFeet(from))
+	{
+		LOGV << "unit has cold feet, order discarded";
+		return discarded(player, order, cset, Notice::COLDFEET);
+	}
+
+	// This unit is now in lockdown mode.
+	_lockdowns.emplace_back(activeunit.id(), from, to);
+
 	// If the cell is empty, we cannot attack.
 	// If the unit is friendly, we cannot attack.
 	if (!otherunit || otherunit.owner == activeunit.owner)
@@ -1920,6 +1946,13 @@ void Automaton::processShell(const Player& player, Order& order)
 		return discarded(player, order, cset, Notice::ORDERINVALID);
 	}
 
+	// Does the unit get cold feet?
+	if (hasColdFeet(from))
+	{
+		LOGV << "unit has cold feet, order discarded";
+		return discarded(player, order, cset, Notice::COLDFEET);
+	}
+
 	// Deal the damage.
 	for (int volley = 0; volley < _bible.unitAbilityVolleys(unittype); volley++)
 	{
@@ -1995,6 +2028,13 @@ void Automaton::processBombard(const Player& player, Order& order)
 		return discarded(player, order, cset, Notice::ORDERINVALID);
 	}
 
+	// Does the unit get cold feet?
+	if (hasColdFeet(from))
+	{
+		LOGV << "unit has cold feet, order discarded";
+		return discarded(player, order, cset, Notice::COLDFEET);
+	}
+
 	// Deal the damage.
 	for (int volley = 0; volley < _bible.unitAbilityVolleys(unittype); volley++)
 	{
@@ -2060,6 +2100,13 @@ void Automaton::processBomb(const Player& player, Order& order)
 		return discarded(player, order, cset, Notice::ORDERINVALID);
 	}
 
+	// Does the unit get cold feet?
+	if (hasColdFeet(at))
+	{
+		LOGV << "unit has cold feet, order discarded";
+		return discarded(player, order, cset, Notice::COLDFEET);
+	}
+
 	// Deal the damage.
 	for (int volley = 0; volley < _bible.unitAbilityVolleys(unittype); volley++)
 	{
@@ -2125,6 +2172,13 @@ void Automaton::processCapture(const Player& player, Order& order)
 		return discarded(player, order, cset, Notice::ORDERINVALID);
 	}
 
+	// Does the unit get cold feet?
+	if (hasColdFeet(at))
+	{
+		LOGV << "unit has cold feet, order discarded";
+		return discarded(player, order, cset, Notice::COLDFEET);
+	}
+
 	// We can't capture a tile that is already ours.
 	if (tile.owner == conqueror.owner)
 	{
@@ -2242,6 +2296,13 @@ void Automaton::processShape(const Player& player, Order& order)
 		return discarded(player, order, cset, Notice::UNBUILDABLE);
 	}
 
+	// Does the unit get cold feet?
+	if (hasColdFeet(at))
+	{
+		LOGV << "unit has cold feet, order discarded";
+		return discarded(player, order, cset, Notice::COLDFEET);
+	}
+
 	// If the player cannot afford the unit cost, the order is postponed.
 	if (_money[player] < build.cost)
 	{
@@ -2365,6 +2426,13 @@ void Automaton::processSettle(const Player& player, Order& order)
 		return discarded(player, order, cset, Notice::UNBUILDABLE);
 	}
 
+	// Does the unit get cold feet?
+	if (hasColdFeet(at))
+	{
+		LOGV << "unit has cold feet, order discarded";
+		return discarded(player, order, cset, Notice::COLDFEET);
+	}
+
 	// If the player cannot afford the unit cost, the order is postponed.
 	if (_money[player] < build.cost)
 	{
@@ -2410,6 +2478,7 @@ void Automaton::processSettle(const Player& player, Order& order)
 	checkTileBuildMoraleGain(at, cset);
 
 	// Check for cleanses.
+	checkColdFeetCleanse(at, cset);
 	checkTileBuildCleanse(at, cset);
 
 	// Check for auto-cultivate triggers.
@@ -3468,6 +3537,9 @@ void Automaton::doMove(Cell from, Cell to,
 		changes.push(exitchange, unsees);
 	}
 
+	// After we move, cold feet wears off.
+	checkColdFeetCleanse(from, changes);
+
 	// After we move, we check for trample damage.
 	// If there is any trample damage, it takes place in the same changeset.
 	checkTrample(to, todesc, changes);
@@ -3539,7 +3611,7 @@ void Automaton::doActiveAttack(Cell from, Cell to,
 
 	// If the defending unit was not killed during the attack and can retaliate, it will.
 	const UnitToken& takingunit = _board.unit(to, taker.type);
-	if (takingunit && _bible.unitCanAttack(takingunit.type))
+	if (takingunit && _bible.unitCanAttack(takingunit.type) && !hasColdFeet(to))
 	{
 		doRetaliationAttack(to, from, taker, attacker, changes);
 	}
@@ -3637,7 +3709,8 @@ void Automaton::doFocussedAttack(Cell from, Cell to,
 
 		// Get the ground unit of that tile (only ground units can attack).
 		const UnitToken& unit = _board.ground(at);
-		if (!unit || !_bible.unitCanAttack(unit.type)) continue;
+		if (!unit || !_bible.unitCanAttack(unit.type)
+			|| hasColdFeet(at)) continue;
 
 		// Only units belonging to the player that gave the order respond to it.
 		if (unit.owner != focussingunit.owner) continue;
@@ -3686,7 +3759,7 @@ void Automaton::doFocussedAttack(Cell from, Cell to,
 
 	// If the defending unit was not killed during the attack and can retaliate, it will.
 	const UnitToken& takingunit = _board.unit(to, taker.type);
-	if (takingunit && _bible.unitCanAttack(takingunit.type))
+	if (takingunit && _bible.unitCanAttack(takingunit.type) && !hasColdFeet(to))
 	{
 		doRetaliationAttack(to, from, taker, attacker, changes);
 	}
@@ -3715,7 +3788,8 @@ void Automaton::checkAttackOfOpportunity(Cell at,
 	{
 		// Get the ground unit of that tile (only ground units can attack).
 		const UnitToken& unit = _board.ground(from);
-		if (!unit || !_bible.unitCanAttack(unit.type)) continue;
+		if (!unit || !_bible.unitCanAttack(unit.type)
+			|| hasColdFeet(from)) continue;
 		if (unit.owner == movingunit.owner) continue;
 
 		// The attacker aims.
@@ -3800,7 +3874,7 @@ bool Automaton::checkLockdown(Cell at,
 		lockdown = true;
 
 		// The lockdown unit may or may not also be able to attack.
-		if (!_bible.unitCanAttack(unit.type)) continue;
+		if (!_bible.unitCanAttack(unit.type) || hasColdFeet(from)) continue;
 
 		// The attacker aims.
 		changes.push(Change(Change::Type::AIMS,
@@ -4210,6 +4284,9 @@ void Automaton::doUnitDeath(Cell at, const UnitToken& unit,
 	_board.enact(deathchange);
 	changes.push(deathchange, _board.vision(at));
 
+	// Check cleanses.
+	checkColdFeetCleanse(at, changes);
+
 	// Some units release gas or radation on destruction.
 	checkUnitDeathLeak(at, oldtype, changes);
 
@@ -4534,8 +4611,27 @@ void Automaton::doDeathEffect(Cell at)
 
 void Automaton::doFrostbiteEffect(Cell at)
 {
+	if (_bible.frostbiteGivesColdFeet()
+		&& _board.frostbite(at) && _board.ground(at)
+		// Frostbite's Cold Feet is applied in Winter, not in Spring.
+		&& _bible.chaosMinFrostbite(_season) >= 0)
+	{
+		ChangeSet cset;
+		for (int figure = 0; figure < _board.ground(at).stacks; figure++)
+		{
+			// The FROSTBITTEN change tells a player that a unit was bitten
+			// by frostbite.
+			Change change(Change::Type::FROSTBITTEN,
+				Descriptor::ground(at.pos()),
+				figure, /*killing=*/false, /*depowering=*/false);
+			_board.enact(change);
+			cset.push(change, _board.vision(at));
+		}
+		_changesets.push(cset);
+	}
+
 	// Is there enough frostbite to do damage?
-	if (_board.frostbite(at) < _bible.frostbiteThresholdDamage()) return;
+	if ((_board.frostbite(at) ? 1 : 0) < _bible.frostbiteThresholdDamage()) return;
 
 	// Frostbite no longer affects tiles or air.
 	bool hittiles = !_bible.frostbiteOnlyTargetsGroundUnits();
@@ -4798,6 +4894,30 @@ void Automaton::doRadiationEffect(Cell at)
 	_changesets.push(cset);
 }
 
+bool Automaton::hasColdFeet(Cell at)
+{
+	return (_bible.frostbiteGivesColdFeet()
+		&& _board.frostbite(at) && _board.ground(at)
+		// Frostbite's Cold Feet effect applies in Spring, not in Winter.
+		&& _bible.chaosMinFrostbite(_season) < 0);
+}
+
+void Automaton::checkColdFeetCleanse(Cell at, ChangeSet& changes)
+{
+	if (_bible.frostbiteGivesColdFeet()
+		// Once the unit moves away or is killed, Cold Feet wears off.
+		&& _board.frostbite(at) && !_board.ground(at)
+		// But only in Spring, not in Winter.
+		&& _bible.chaosMinFrostbite(_season) < 0)
+	{
+		Change change(Change::Type::FROSTBITE,
+			Descriptor::cell(at.pos()));
+		change.xFrostbite(false);
+		_board.enact(change);
+		changes.push(change, _board.vision(at));
+	}
+}
+
 void Automaton::decay()
 {
 	{
diff --git a/epicinium/src/logic/automaton.hpp b/epicinium/src/logic/automaton.hpp
index 127b932..0cb9023 100644
--- a/epicinium/src/logic/automaton.hpp
+++ b/epicinium/src/logic/automaton.hpp
@@ -186,6 +186,8 @@ class Automaton : private PlayerInfo, private RoundInfo
 	void doFirestormEffect(Cell at);
 	void doGasEffect(Cell at);
 	void doRadiationEffect(Cell at);
+	bool hasColdFeet(Cell at);
+	void checkColdFeetCleanse(Cell at, ChangeSet& changes);
 
 	void checkRegularDefeat();
 	void checkChallengeDefeat();
diff --git a/epicinium/src/logic/bible.cpp b/epicinium/src/logic/bible.cpp
index e219f4f..99368e4 100644
--- a/epicinium/src/logic/bible.cpp
+++ b/epicinium/src/logic/bible.cpp
@@ -292,6 +292,7 @@ Bible::Bible(const std::string& name, const Version& version) :
 	_moraleGatheredInSummer(false),
 	_moraleGatheredWhenBuilt(false),
 	_snowCoversNiceness(false),
+	_frostbiteGivesColdFeet(false),
 	_snowSlowAmount(0),
 	_snowSlowMaximum(0),
 	_startingMoney(0),
@@ -393,7 +394,7 @@ void Bible::initialize()
 	_tileNatural[i] = true;
 	_tilePlane[i] = true;
 	_tileFlammable[i] = true;
-	//_tileFirestormResistance[i] = 10;
+	_tileFirestormResistance[i] = 10;
 	_tileRegrowOnlyInSpring[i] = true;
 	_tileRegrowthProbabilityDivisor[i] = 4;
 	_tileRegrowthAmount[i] = 1;
@@ -466,7 +467,7 @@ void Bible::initialize()
 	_tileGrassy[i] = true;
 	_tileNatural[i] = true;
 	_tileFlammable[i] = true;
-	//_tileFirestormResistance[i] = 10;
+	_tileFirestormResistance[i] = 10;
 	_tileChaosProtection[i] = true;
 	_tileRegrowOnlyInSpring[i] = true;
 	_tileStacksBuilt[i] = 1;
@@ -498,8 +499,8 @@ void Bible::initialize()
 	_tileHitpoints[i] = 2;
 	_tileIncome[i] = 1;
 	_tileEmission[i] = 2;
-	//_tileFlammable[i] = true;
-	//_tileFirestormResistance[i] = 70;
+	_tileFlammable[i] = true;
+	_tileFirestormResistance[i] = 70;
 	_tileProduces[i] = {{(UnitType) MILITIA, 10}, (UnitType) SETTLER};
 	_tileExpands[i] = {(TileType) INDUSTRY, (TileType) BARRACKS};
 	_tileCost[i] = 50;
@@ -524,8 +525,8 @@ void Bible::initialize()
 	_tileHitpoints[i] = 2;
 	_tileIncome[i] = 1;
 	_tileEmission[i] = 1;
-	//_tileFlammable[i] = true;
-	//_tileFirestormResistance[i] = 70;
+	_tileFlammable[i] = true;
+	_tileFirestormResistance[i] = 70;
 	_tileProduces[i] = {(UnitType) SETTLER};
 	_tileUpgrades[i] = {{TileType::NONE, 4}, {(TileType) CITY, 40}};
 	_tileCost[i] = 10;
@@ -550,8 +551,8 @@ void Bible::initialize()
 	_tileHitpoints[i] = 2;
 	_tileIncome[i] = 0;
 	_tileEmission[i] = 1;
-	//_tileFlammable[i] = true;
-	//_tileFirestormResistance[i] = 70;
+	_tileFlammable[i] = true;
+	_tileFirestormResistance[i] = 70;
 	_tileProduces[i] = {(UnitType) SETTLER, (UnitType) MILITIA};
 	_tileUpgrades[i] = {};
 	_tileCost[i] = 0;
@@ -579,8 +580,8 @@ void Bible::initialize()
 	_tileEmission[i] = 5;
 	_tilePollutionAmount[i] = 1;
 	_tilePollutionRadius[i] = 2;
-	//_tileFlammable[i] = true;
-	//_tileFirestormResistance[i] = 70;
+	_tileFlammable[i] = true;
+	_tileFirestormResistance[i] = 70;
 	_tileProduces[i] = {(UnitType) TANK};
 	_tileExpands[i] = {(TileType) AIRFIELD};
 	_tileUpgrades[i] = {{TileType::NONE, 50}};
@@ -604,8 +605,8 @@ void Bible::initialize()
 	_tileVision[i] = 2;
 	_tileHitpoints[i] = 3;
 	_tileEmission[i] = 1;
-	//_tileFlammable[i] = true;
-	//_tileFirestormResistance[i] = 70;
+	_tileFlammable[i] = true;
+	_tileFirestormResistance[i] = 70;
 	_tileProduces[i] = {(UnitType) RIFLEMAN, (UnitType) GUNNER, (UnitType) SAPPER};
 	_tileUpgrades[i] = {{TileType::NONE, 25}};
 	_tileCost[i] = 5;
@@ -629,8 +630,8 @@ void Bible::initialize()
 	_tileHitpoints[i] = 3;
 	_tileLeakGas[i] = 1;
 	_tileEmission[i] = 1;
-	//_tileFlammable[i] = true;
-	//_tileFirestormResistance[i] = 70;
+	_tileFlammable[i] = true;
+	_tileFirestormResistance[i] = 70;
 	_tileProduces[i] = {(UnitType) ZEPPELIN};
 	_tileCost[i] = 5;
 	_tileDestroyed[i] = (TileType) RUBBLE;
@@ -654,8 +655,8 @@ void Bible::initialize()
 	_tileHitpoints[i] = 2;
 	_tileIncome[i] = 0;
 	_tileEmission[i] = 1;
-	//_tileFlammable[i] = true;
-	//_tileFirestormResistance[i] = 70;
+	_tileFlammable[i] = true;
+	_tileFirestormResistance[i] = 70;
 	_tileProduces[i] = {(UnitType) SETTLER, (UnitType) MILITIA};
 	_tileCultivates[i] = {(TileType) SOIL};
 	_tileCost[i] = 5;
@@ -673,7 +674,7 @@ void Bible::initialize()
 	_tileNatural[i] = false;
 	_tilePlane[i] = true;
 	_tileFlammable[i] = true;
-	//_tileFirestormResistance[i] = 10;
+	_tileFirestormResistance[i] = 10;
 	_tileRegrowOnlyInSpring[i] = false;
 	_tileVision[i] = 0;
 	_tileIncome[i] = 0;
@@ -695,7 +696,7 @@ void Bible::initialize()
 	_tileNatural[i] = true;
 	_tilePlane[i] = true;
 	_tileFlammable[i] = true;
-	//_tileFirestormResistance[i] = 10;
+	_tileFirestormResistance[i] = 10;
 	_tileVision[i] = 0;
 	_tileIncome[i] = 1;
 	_tileDestroyed[i] = (TileType) DIRT;
@@ -713,7 +714,7 @@ void Bible::initialize()
 	_tileControllable[i] = false;
 	_tilePlane[i] = false;
 	_tileFlammable[i] = true;
-	//_tileFirestormResistance[i] = 10;
+	_tileFirestormResistance[i] = 10;
 	_tileTrenches[i] = true;
 	_tileForceOccupy[i] = true;
 	_tileCost[i] = 0;
@@ -872,7 +873,6 @@ void Bible::initialize()
 	_aridificationRange = 2;
 
 	_aridificationCount = 4;
-	_firestormCount = 5;
 	_deathCount = 1;
 
 	_humidityMax = 4;
@@ -906,7 +906,7 @@ void Bible::initialize()
 	_humidityMaxDegradation[i] = 0;
 	_humidityMaxDesertification[i] = 0;
 	_humidityMinSnow[i] = 4;
-	_humidityMaxFirestorm[i] = 4;
+	_humidityMaxFirestorm[i] = 3;
 	_humidityMaxBonedrought[i] = 0;
 	_humidityMaxStonedrought[i] = 0;
 	_chaosMinDegradation[i] = 0;
@@ -954,15 +954,13 @@ void Bible::initialize()
 	_chaosMinStonedrought[i] = 4 * _chaosThreshold;
 	_chaosMinDeath[i] = -1;
 
-	_frostbiteShots = 2;
-	_frostbiteDamage = 1;
-	_frostbiteThresholdDamage = 1;
+	_frostbiteThresholdDamage = 100;
 	_frostbiteThresholdVulnerability = 100;
 
 	_firestormShots = 3;
 	_firestormDamage = 2;
-	//_firestormBasePercentage = 30;
-	//_firestormDroughtPercentage = 20;
+	_firestormBasePercentage = 30;
+	_firestormDroughtPercentage = 20;
 
 	_gasShots = 3;
 	_gasDamage = 1;
@@ -1009,9 +1007,8 @@ void Bible::initialize()
 	_emptyBasedFrostbite = false;
 	_planeBasedFrostbite = true;
 	_planeBasedAridification = true;
-	_flammableBasedFirestorm = true;
-	_percentageBasedFirestorm = false;
-	_randomizedFirestorm = true;
+	_percentageBasedFirestorm = true;
+	_randomizedFirestorm = false;
 	_randomizedAridification = true;
 	_cumulativeDeath = true;
 	_vulnerabilitiesStack = true;
@@ -1023,6 +1020,7 @@ void Bible::initialize()
 	_moraleGatheredInSummer = false;
 	_moraleGatheredWhenBuilt = false;
 	_snowCoversNiceness = true;
+	_frostbiteGivesColdFeet = true;
 
 	_snowSlowAmount = 1;
 	_snowSlowMaximum = 1;
@@ -1034,12 +1032,29 @@ void Bible::initialize()
 
 void Bible::customize()
 {
-	const size_t CITY = (size_t) tiletype("city");
+	//const size_t CITY = (size_t) tiletype("city");
+	const size_t TOWN = (size_t) tiletype("town");
+	const size_t FARM = (size_t) tiletype("farm");
 	const size_t BARRACKS = (size_t) tiletype("barracks");
-	const size_t RIFLEMAN = (size_t) unittype("rifleman");
-
-	_tileExpands[CITY] = {(TileType) BARRACKS};
-	_tileProduces[BARRACKS] = {(UnitType) RIFLEMAN};
+	const size_t INDUSTRY = (size_t) tiletype("industry");
+	//const size_t RIFLEMAN = (size_t) unittype("rifleman");
+	const size_t GUNNER = (size_t) unittype("gunner");
+	//const size_t MILITIA = (size_t) unittype("militia");
+	const size_t SETTLER = (size_t) unittype("settler");
+	const size_t SAPPER = (size_t) unittype("sapper");
+
+	//_tileProduces[CITY] = {(UnitType) SETTLER, {((UnitType) RIFLEMAN), 25}};
+	_tileUpgrades[TOWN] = {};
+	_tileGrowthMax[TOWN] = 5;
+	_tileProduces[BARRACKS] = {(UnitType) SAPPER, (UnitType) GUNNER};
+	_unitCost[SAPPER] = 20;
+	_unitCost[GUNNER] = 25;
+	_tileUpgrades[BARRACKS] = {};
+	_tileUpgrades[INDUSTRY] = {};
+	_tileExpands[INDUSTRY] = {};
+	_unitSettles[SETTLER] = {(TileType) TOWN, (TileType) FARM};
+	_unitCanLockdown[GUNNER] = false;
+	//_unitShapes[RIFLEMAN] = {};
 }
 
 void Bible::finalize()
@@ -2263,6 +2278,7 @@ Bible::Bible(const std::string& biblename, const Json::Value& json) :
 		}
 	}
 	AUTO(PARSEBOOL, snowCoversNiceness)
+	AUTO(PARSEBOOL, frostbiteGivesColdFeet)
 
 	AUTO(PARSEINT, snowSlowAmount)
 	else
@@ -2278,14 +2294,14 @@ Bible::Bible(const std::string& biblename, const Json::Value& json) :
 	}
 	// Backwards compatiblity: trenches had their slow amount hardcoded.
 	{
-		bool trenchesSlowAmount;
+		int trenchesSlowAmount;
 		PARSEINT(trenchesSlowAmount, "trenchesSlowAmount")
 		else
 		{
 			// Backwards compatibility.
 			trenchesSlowAmount = 10;
 		}
-		if (trenchesSlowAmount)
+		if (trenchesSlowAmount > 0)
 		{
 			TileType trenchestype = tiletype("trenches");
 			if (trenchestype != TileType::NONE)
@@ -2296,14 +2312,14 @@ Bible::Bible(const std::string& biblename, const Json::Value& json) :
 	}
 	// Backwards compatiblity: trenches had their slow maximum hardcoded.
 	{
-		bool trenchesSlowMaximum;
+		int trenchesSlowMaximum;
 		PARSEINT(trenchesSlowMaximum, "trenchesSlowMaximum")
 		else
 		{
 			// Backwards compatibility.
 			trenchesSlowMaximum = 10;
 		}
-		if (trenchesSlowMaximum)
+		if (trenchesSlowMaximum > 0)
 		{
 			TileType trenchestype = tiletype("trenches");
 			if (trenchestype != TileType::NONE)
@@ -2897,6 +2913,7 @@ Json::Value Bible::toJson() const
 	AUTO(PUTBOOL, moraleGatheredInSummer)
 	AUTO(PUTBOOL, moraleGatheredWhenBuilt)
 	AUTO(PUTBOOL, snowCoversNiceness)
+	AUTO(PUTBOOL, frostbiteGivesColdFeet)
 
 	AUTO(FORCEPUTINT, snowSlowAmount) // Backwards compatibility.
 	AUTO(FORCEPUTINT, snowSlowMaximum) // Backwards compatibility.
@@ -3275,6 +3292,7 @@ bool Bible::operator==(const Bible& other) const
 	AUTO(CHECK, moraleGatheredInSummer)
 	AUTO(CHECK, moraleGatheredWhenBuilt)
 	AUTO(CHECK, snowCoversNiceness)
+	AUTO(CHECK, frostbiteGivesColdFeet)
 
 	AUTO(CHECK, snowSlowAmount)
 	AUTO(CHECK, snowSlowMaximum)
diff --git a/epicinium/src/logic/bible.hpp b/epicinium/src/logic/bible.hpp
index 2449251..bcbf55c 100644
--- a/epicinium/src/logic/bible.hpp
+++ b/epicinium/src/logic/bible.hpp
@@ -359,6 +359,7 @@ class Bible : public TypeNamer
 	bool _moraleGatheredInSummer;
 	bool _moraleGatheredWhenBuilt;
 	bool _snowCoversNiceness;
+	bool _frostbiteGivesColdFeet;
 
 	int8_t _snowSlowAmount;
 	int8_t _snowSlowMaximum;
@@ -663,6 +664,7 @@ class Bible : public TypeNamer
 	bool moraleGatheredInSummer()            const { return _moraleGatheredInSummer;           }
 	bool moraleGatheredWhenBuilt()           const { return _moraleGatheredWhenBuilt;          }
 	bool snowCoversNiceness()                const { return _snowCoversNiceness;      }
+	bool frostbiteGivesColdFeet()                const { return _frostbiteGivesColdFeet;      }
 
 	int8_t snowSlowAmount()            const { return _snowSlowAmount;              }
 	int8_t snowSlowMaximum()           const { return _snowSlowMaximum;             }
diff --git a/epicinium/src/logic/board.cpp b/epicinium/src/logic/board.cpp
index a88cd1a..e7984f0 100644
--- a/epicinium/src/logic/board.cpp
+++ b/epicinium/src/logic/board.cpp
@@ -78,9 +78,30 @@ void Board::load(const std::string& mapname)
 	std::string line;
 
 	std::string fname = Map::readOnlyFilename(mapname);
+	if (!System::isFile(fname))
+	{
+		LOGF << "Failed to load map '" << mapname << "' (" << fname << "): "
+			<< "file does not exist";
+		throw std::runtime_error("failed to load map " + mapname + ": \t"
+				+ "file does not exist");
+	}
+
 	std::ifstream file = System::ifstream(fname);
-	if (!std::getline(file, line) || !reader.parse(line, metadata)
-		|| !metadata.isObject())
+	if (!file)
+	{
+		LOGF << "Failed to load map '" << mapname << "' (" << fname << "): "
+			<< "failed to open file";
+		throw std::runtime_error("failed to load map " + mapname + ": \t"
+				+ "failed to open file");
+	}
+	else if (!std::getline(file, line) || line.empty())
+	{
+		LOGF << "Failed to load map '" << mapname << "' (" << fname << "): "
+			<< "failed to read line";
+		throw std::runtime_error("failed to load map " + mapname + ": \t"
+				+ "failed to read line");
+	}
+	else if (!reader.parse(line, metadata) || !metadata.isObject())
 	{
 		// Try old style.
 		file.close();
diff --git a/epicinium/src/logic/damage.cpp b/epicinium/src/logic/damage.cpp
index 190db18..574c9c1 100644
--- a/epicinium/src/logic/damage.cpp
+++ b/epicinium/src/logic/damage.cpp
@@ -286,7 +286,7 @@ int Damage::hitpoints(Cell index, const TileToken& tile)
 	int loss = 0;
 
 	// Frostbite only affects ground units.
-	if (_board.frostbite(index) >= _bible.frostbiteThresholdVulnerability()
+	if ((_board.frostbite(index) ? 1 : 0) >= _bible.frostbiteThresholdVulnerability()
 			&& !_bible.frostbiteOnlyTargetsGroundUnits())
 	{
 		loss++;
@@ -333,7 +333,7 @@ int Damage::hitpoints(Cell index, const UnitToken& unit)
 	int loss = 0;
 
 	// Frostbite affects everything.
-	if (_board.frostbite(index) >= _bible.frostbiteThresholdVulnerability()
+	if ((_board.frostbite(index) ? 1 : 0) >= _bible.frostbiteThresholdVulnerability()
 			&& (!_bible.frostbiteOnlyTargetsGroundUnits()
 				|| !_bible.unitAir(unit.type)))
 	{
diff --git a/epicinium/src/logic/gameowner.hpp b/epicinium/src/logic/gameowner.hpp
index 0c73d7f..340f9ed 100644
--- a/epicinium/src/logic/gameowner.hpp
+++ b/epicinium/src/logic/gameowner.hpp
@@ -48,7 +48,8 @@ class GameOwner
 	virtual ~GameOwner() = default;
 
 	virtual std::weak_ptr<Game> startGame(imploding_ptr<Game> game) = 0;
-	virtual std::weak_ptr<Game> startChallenge(const Challenge& challenge) = 0;
+	virtual std::weak_ptr<Game> startChallenge(const Challenge& challenge,
+		const std::string& name = "") = 0;
 	virtual std::weak_ptr<Game> startGame(
 		const Player& player, const std::string& rulesetname,
 		uint32_t planningTime) = 0;
@@ -69,4 +70,6 @@ class GameOwner
 		const std::string& mapname, const std::string& rulesetname) = 0;
 
 	virtual void stopGame() = 0;
+
+	virtual void reportAwardedStars(int /*amount*/) {};
 };
diff --git a/epicinium/src/logic/map.cpp b/epicinium/src/logic/map.cpp
index 4225030..dc0a892 100644
--- a/epicinium/src/logic/map.cpp
+++ b/epicinium/src/logic/map.cpp
@@ -129,6 +129,14 @@ std::string Map::authoredFilename(const std::string& name)
 
 Json::Value Map::loadMetadata(const std::string& name)
 {
+	for (const auto& item : _cachedexternalitems)
+	{
+		if (item.uniqueTag == name)
+		{
+			return item.metadata;
+		}
+	}
+
 	try
 	{
 		std::ifstream file = System::ifstream(readOnlyFilename(name));
diff --git a/epicinium/src/logic/map.hpp b/epicinium/src/logic/map.hpp
index 9833769..326190e 100644
--- a/epicinium/src/logic/map.hpp
+++ b/epicinium/src/logic/map.hpp
@@ -47,6 +47,7 @@ class Map
 		std::string uniqueTag;
 		std::string quotedName;
 		std::string sourceFilename;
+		Json::Value metadata;
 	};
 
 private:
diff --git a/epicinium/src/logic/markertransition.cpp b/epicinium/src/logic/markertransition.cpp
index 65c5d01..db02a2d 100644
--- a/epicinium/src/logic/markertransition.cpp
+++ b/epicinium/src/logic/markertransition.cpp
@@ -39,6 +39,7 @@ namespace MarkerFlag
 		FIRESTORM = 0x04,
 		BONEDROUGHT = 0x08,
 		DEATH = 0x10,
+		COLDFEET = 0x20,
 	};
 }
 
@@ -152,10 +153,16 @@ void MarkerTransition::execute()
 	}
 }
 
+constexpr Season previousSeason(const Season& season)
+{
+	return (Season) ((((size_t) season) + SEASON_SIZE - 1) % SEASON_SIZE);
+}
+
 void MarkerTransition::map(Cell index)
 {
 	bool snow;
 	bool frostbite;
+	bool coldfeet;
 	bool firestorm;
 	bool bonedrought;
 	bool death;
@@ -184,6 +191,9 @@ void MarkerTransition::map(Cell index)
 				: (_bible.stackBasedFrostbite())
 				? ((stacks + 1) * _bible.chaosMinFrostbite(_season) <= chaos)
 				: true));
+		coldfeet = (_bible.frostbiteGivesColdFeet()
+				&& _board.frostbite(index) && _board.ground(index)
+				&& _bible.chaosMinFrostbite(previousSeason(_season)) >= 0);
 		firestorm = (_bible.chaosMinFirestorm(_season) >= 0
 			&& !_bible.randomizedFirestorm()
 			&& !_bible.percentageBasedFirestorm()
@@ -245,6 +255,7 @@ void MarkerTransition::map(Cell index)
 			&& temp <= _bible.temperatureMaxSnow(_season);
 		// Frostbite occurs if the temperature is critically low.
 		frostbite = temp <= _bible.temperatureMaxFrostbite(_season);
+		coldfeet = false;
 		// Firestorm occurs if the temperature is critically high.
 		firestorm = temp >= _bible.temperatureMinFirestorm(_season);
 		// Bonedrought occurs if the humidity is critically low.
@@ -259,6 +270,7 @@ void MarkerTransition::map(Cell index)
 	uint8_t result = 0;
 	if (snow) result |= MarkerFlag::SNOW;
 	if (frostbite) result |= MarkerFlag::FROSTBITE;
+	if (coldfeet) result |= MarkerFlag::COLDFEET;
 	if (firestorm) result |= MarkerFlag::FIRESTORM;
 	if (bonedrought) result |= MarkerFlag::BONEDROUGHT;
 	if (death) result |= MarkerFlag::DEATH;
@@ -283,11 +295,17 @@ void MarkerTransition::reduce(Cell index)
 
 	{
 		bool frostbite = (result & MarkerFlag::FROSTBITE);
-		if (frostbite != _board.frostbite(index))
+		bool coldfeet = (result & MarkerFlag::COLDFEET);
+		// Frostbite freezes ground units in Winter. This is implemented by
+		// having it stick around until Spring or until the unit moves.
+		// We issue a second positive FROSTBITE update when this happens, to
+		// help with animations.
+		if (frostbite != _board.frostbite(index)
+			|| (frostbite || coldfeet) != _board.frostbite(index))
 		{
 			Change change(Change::Type::FROSTBITE,
 				Descriptor::cell(index.pos()));
-			change.xFrostbite(frostbite);
+			change.xFrostbite(frostbite || coldfeet);
 			_board.enact(change);
 			_changeset.push(change, _board.vision(index));
 		}
diff --git a/epicinium/src/logic/notice.cpp b/epicinium/src/logic/notice.cpp
index 3d41126..9be3321 100644
--- a/epicinium/src/logic/notice.cpp
+++ b/epicinium/src/logic/notice.cpp
@@ -43,6 +43,7 @@ Notice parseNotice(const std::string& str)
 	else if (str == "lackingstacks")       return Notice::LACKINGSTACKS;
 	else if (str == "lackingpower")        return Notice::LACKINGPOWER;
 	else if (str == "lackingmoney")        return Notice::LACKINGMONEY;
+	else if (str == "coldfeet")            return Notice::COLDFEET;
 	else if (str == "occupiedbyenemy")     return Notice::OCCUPIEDBYENEMY;
 	else if (str == "activeattack") return Notice::ACTIVEATTACK;
 	else if (str == "retaliationattack") return Notice::RETALIATIONATTACK;
@@ -73,6 +74,7 @@ const char* stringify(const Notice& notice)
 		case Notice::LACKINGSTACKS:       return "lackingstacks";
 		case Notice::LACKINGPOWER:        return "lackingpower";
 		case Notice::LACKINGMONEY:        return "lackingmoney";
+		case Notice::COLDFEET:            return "coldfeet";
 		case Notice::OCCUPIEDBYENEMY:     return "occupiedbyenemy";
 		case Notice::ACTIVEATTACK: return "activeattack";
 		case Notice::RETALIATIONATTACK: return "retaliationattack";
diff --git a/epicinium/src/logic/notice.hpp b/epicinium/src/logic/notice.hpp
index d7061ed..497b67d 100644
--- a/epicinium/src/logic/notice.hpp
+++ b/epicinium/src/logic/notice.hpp
@@ -41,6 +41,7 @@ enum class Notice : uint8_t
 	LACKINGSTACKS,
 	LACKINGPOWER,
 	LACKINGMONEY,
+	COLDFEET,
 	OCCUPIEDBYENEMY,
 	ACTIVEATTACK,
 	RETALIATIONATTACK,
diff --git a/epicinium/src/logic/position.hpp b/epicinium/src/logic/position.hpp
index 9f79936..05c56f1 100644
--- a/epicinium/src/logic/position.hpp
+++ b/epicinium/src/logic/position.hpp
@@ -30,8 +30,13 @@ struct Position
 	// The board size must be strictly smaller than 128x128 because we use
 	// int8_t to store _rows in Cell, so it can have values 1 to 127 inclusive.
 	// We use a much smaller maximum value to help train neural networks.
+#if NEURALNEWT_20x13_ENABLED
+	static constexpr int MAX_COLS = 20;
+	static constexpr int MAX_ROWS = 13;
+#else
 	static constexpr int MAX_COLS = 32;
 	static constexpr int MAX_ROWS = MAX_COLS;
+#endif
 
 	int8_t row;
 	int8_t col;
diff --git a/epicinium/src/logic/tiletype.hpp b/epicinium/src/logic/tiletype.hpp
index 30b88ab..aa6c8f7 100644
--- a/epicinium/src/logic/tiletype.hpp
+++ b/epicinium/src/logic/tiletype.hpp
@@ -32,7 +32,11 @@ enum class TileType : uint8_t
 	NONE = 0,
 };
 
+#if NEURALNEWT_20x13_ENABLED
+static constexpr size_t TILETYPE_SIZE = 19;
+#else
 static constexpr size_t TILETYPE_SIZE = 32;
+#endif
 
 TileType parseTileType(const TypeNamer& namer, const std::string& str);
 
diff --git a/epicinium/src/logic/unittype.hpp b/epicinium/src/logic/unittype.hpp
index b5b4170..1c6b8d7 100644
--- a/epicinium/src/logic/unittype.hpp
+++ b/epicinium/src/logic/unittype.hpp
@@ -32,7 +32,11 @@ enum class UnitType : uint8_t
 	NONE = 0,
 };
 
+#if NEURALNEWT_20x13_ENABLED
+static constexpr size_t UNITTYPE_SIZE = 8;
+#else
 static constexpr size_t UNITTYPE_SIZE = 32;
+#endif
 
 UnitType parseUnitType(const TypeNamer& namer, const std::string& str);
 
diff --git a/epicinium/src/logic/visiontransition.cpp b/epicinium/src/logic/visiontransition.cpp
index 14f0cd2..f2ab84a 100644
--- a/epicinium/src/logic/visiontransition.cpp
+++ b/epicinium/src/logic/visiontransition.cpp
@@ -32,6 +32,9 @@
 #include "tiletoken.hpp"
 #include "unittoken.hpp"
 
+ // windows.h is being annoying
+#undef near
+
 
 template <class This>
 VisionTMRI<This>::VisionTMRI(const Bible& bible, Board& board,