Gen 2: Proper interaction of critical hits and burn

Normal damage is calculated with boosts, screens, and burn.
If a critical hit happens, then:
Stat level modifications are ignored if they are neutral to or favour the defender.
Reflect and Light Screen defensive boosts are only ignored if stat level modifications were also ignored as a result thereof.
If the attacker is burned, stat level modifications are always ignored.
The attack drop from the burn is only applied when attacker's attack level is higher than defender's defense level (boost).

Therefor:
A critical hit will ignore defensive and offensive buffs/debuffs if the attacker and the defender have the same boost level or the defender has higher boost.
The boosts will be ignored if the attacker is burned, but if the attacker has more boost than the defender, burn reduction still applies.
Burn reduction won't apply on the first case, buffs being the same or defender having more.

mods/gen2/scripts.js

@@ -6,16 +6,15 @@ exports.BattleScripts = {
 	gen: 2,
 	// BattlePokemon scripts.
 	pokemon: {
-		getStat: function (statName, unboosted, unmodified, burndrop) {
+		getStat: function (statName, unboosted, unmodified) {
 			statName = toId(statName);
 			if (statName === 'hp') return this.maxhp;
 
 			// base stat
 			var stat = this.stats[statName];
 
 			// Stat boosts.
-			// If the attacker is burned, stat level modifications are always ignored.
-			if (!unboosted && (statName !== 'atk' || (statName === 'atk' && this.status !== 'brn'))) {
+			if (!unboosted) {
 				var boost = this.boosts[statName];
 				if (boost > 6) boost = 6;
 				if (boost < -6) boost = -6;
@@ -26,25 +25,21 @@ exports.BattleScripts = {
 					var numerators = [100, 66, 50, 40, 33, 28, 25];
 					stat = Math.floor(stat * numerators[-boost] / 100);
 				}
-			}
 
-			// Stat modifier effects.
-			if (!unmodified) {
+				// On Gen 2 we check modifications here from moves and items
 				var statTable = {atk:'Atk', def:'Def', spa:'SpA', spd:'SpD', spe:'Spe'};
 				var statMod = 1;
 				statMod = this.battle.runEvent('Modify' + statTable[statName], this, null, null, statMod);
 				stat = this.battle.modify(stat, statMod);
+			}
+
+			if (!unmodified) {
 				// Burn attack drop is checked when you get the attack stat upon switch in and used until switch out.
 				if (this.status === 'brn' && statName === 'atk') {
 					stat = this.battle.clampIntRange(Math.floor(stat / 2), 1);
 				}
 			}
 
-			// Critical hits may apply burn even if unmodified is in effect.
-			if (unmodified && burndrop && this.status === 'brn' && statName === 'atk') {
-				stat = this.battle.clampIntRange(Math.floor(stat / 2), 1);
-			}
-
 			// Gen 2 caps stats at 999 and min is 1.
 			stat = this.battle.clampIntRange(stat, 1, 999);
 
@@ -201,26 +196,32 @@ exports.BattleScripts = {
 		if (move.useSourceDefensive) defender = pokemon;
 		var atkType = (move.category === 'Physical')? 'atk' : 'spa';
 		var defType = (move.defensiveCategory === 'Physical')? 'def' : 'spd';
-		var attack = attacker.getStat(atkType);
-		var defense = defender.getStat(defType);
+		var unboosted = false;
+		var noburndrop = false;
 
 		// The move is a critical hit. Several things happen here.
-		// Level is doubled for damage calculation.
-		// Stat level modifications are ignored if they are neutral to or favour the defender.
-		// Reflect and Light Screen defensive boosts are only ignored if stat level modifications were also ignored as a result of that.
 		if (move.crit) {
+			// Level is doubled for damage calculation.
 			level *= 2;
 			if (!suppressMessages) this.add('-crit', target);
-			if (attacker.status === 'brn' || attacker.boosts[atkType] <= defender.boosts[defType]) {
-				move.ignoreOffensive = true;
-				move.ignoreDefensive = true;
+			// If the attacker is burned, stat level modifications are always ignored. This includes screens.
+			if (attacker.status === 'brn') unboosted = true;
+			// Stat level modifications are ignored if they are neutral to or favour the defender.
+			// Reflect and Light Screen defensive boosts are only ignored if stat level modifications were also ignored as a result of that.
+			if (attacker.boosts[atkType] <= defender.boosts[defType]) {
+				unboosted = true;
+				noburndrop = true;
 			}
 		}
-		// Ignore offense only if attack is lower than boosted and modified.
+		// Get stats now.
+		var attack = attacker.getStat(atkType, unboosted, noburndrop);
+		var defense = defender.getStat(defType, unboosted);
+
+		// Moves that ignore offense and defense respectively.
 		if (move.ignoreOffensive) {
 			this.debug('Negating (sp)atk boost/penalty.');
 			// The attack drop from the burn is only applied when attacker's attack level is higher than defender's defense level.
-			attack = attacker.getStat(atkType, true, true, attack > defense);
+			attack = attacker.getStat(atkType, true, true);
 		}
 		if (move.ignoreDefensive) {
 			this.debug('Negating (sp)def boost/penalty.');
@@ -231,7 +232,6 @@ exports.BattleScripts = {
 		// This is what cuases the roll over bugs.
 		if (attack >= 256 || defense >= 256) {
 			attack = this.clampIntRange(Math.floor(attack / 4) % 256, 1);
-			// Defense isn't checked on the cartridge, but we don't want those / 0 bugs on the sim.
 			defense = this.clampIntRange(Math.floor(defense / 4) % 256, 1);
 		}