Mobtimizer

A Fabric mod for Minecraft 26.2 that merges same-kind mobs into a single ticking entity carrying a member count, cutting the performance cost of large farms without changing how those farms behave.

Merged members stay in the world as real, frozen entities rather than being deleted and counted. That is the design's central bet: removing the mod gives you back every mob, instead of leaving you with one cow where a farm used to be.

Status

Phase 1 complete. Mobs merge, members are kept as frozen entities, counts show on hover, breeding still works, and /mobtimizer unstack restores everything.

Phase 1 is about making stacking correct and safe, not about scaling every mechanic. The full design — where a 100-cow stack breeds, dies and produces like 100 real cows — spans six phases; see the design spec.

Works now	Not yet
Same-kind mobs merge once a crowd forms	Damage routing by source (phase 2)
Members stay real, frozen entities	Scaled breeding — 100 wheat → 50 babies (phase 3)
Count shown on hover	Scaled production: milk, wool, eggs (phase 4)
Babies and breeding animals stay unstacked	Virtual (non-entity) storage for huge stacks (phase 5)
Vanilla two-animal breeding	Mob-cap reporting (phase 6)
Host death promotes a member
Survives world reload
/mobtimizer commands

Verified in play-testing on cows and sheep.

How breeding behaves today

Feeding a stacked animal releases one member as a partner and puts that animal in love — never the stack itself. Feed it, feed the partner, and they breed exactly like two loose animals. Both parents then sit out their normal cooldown unstacked, and rejoin the herd automatically once it expires. The calf stays loose until it grows up.

Feeding a 100-stack does not yet yield 50 babies. That is phase 3.

Requirements

Minecraft	26.2
Fabric Loader	0.19.3 or newer
Fabric API	0.158.0+26.2
Java	25+

Works on a server with completely vanilla clients connected — the count label uses the mob's ordinary custom name, so nothing client-side is required. It also runs fine in single-player.

Installation

You need two jars in your mods folder: Mobtimizer and Fabric API. Fabric API is not bundled.

Single-player / client

1. Install Fabric Loader for Minecraft 26.2.
2. Download mobtimizer-0.1.0.jar from the Releases page.
3. Drop it and Fabric API into your mods folder:
   • Vanilla launcher — %APPDATA%\.minecraft\mods (Windows), ~/Library/Application Support/minecraft/mods (macOS), ~/.minecraft/mods (Linux)
   • PrismLauncher / MultiMC — right-click the instance → Edit → Mods → Add file
   • Modrinth / CurseForge app — the instance's own mods folder
4. Launch the Fabric profile for 26.2.

Confirm it loaded: the log prints Mobtimizer initialising, and the mod appears in Mod Menu if you have it.

Dedicated server

1. Install the Fabric server launcher for 26.2.
2. Put mobtimizer-0.1.0.jar and Fabric API in the server's mods folder.
3. Restart the server.

Clients need nothing.

Building from source

Requires a JDK 25. No JDK on your PATH? Point JAVA_HOME at one — for example the JBR bundled with Android Studio:

JAVA_HOME="/c/Program Files/Android/Android Studio/jbr" ./gradlew build

The jar lands in build/libs/mobtimizer-0.1.0.jar.

Take the plain mobtimizer-0.1.0.jar — not mobtimizer-0.1.0-sources.jar, which sits beside it and contains no compiled classes. Fabric will recognise the sources jar as a mod because it carries a fabric.mod.json, then fail to find any code in it.

./gradlew runClient launches a dev client with the mod already loaded, which is usually faster than building and copying while iterating.

Mod icon

The icon lives at src/main/resources/assets/mobtimizer/icon.png (256×256), with the vector source kept at docs/assets/icon.svg. To change it, replace the PNG and rebuild — Mod Menu picks it up automatically.

Commands

/mobtimizer unstack all	Release every stacked mob in the current level
/mobtimizer unstack here [radius]	Release stacks within radius blocks (default 16)
/mobtimizer unstack type <id>	Release stacks of one entity type, e.g. minecraft:cow
/mobtimizer stats	Report how many mobs are held in how many stacks
/mobtimizer reload	Re-read the config file

All require permission level 2 (gamemasters).

Configuration

config/mobtimizer.json, created on first run. /mobtimizer reload applies changes without a restart.

Setting	Default	What it does
merge.enabled	true	Master switch for merging
merge.radius	8.0	How far apart mobs can be and still merge
merge.crowdThreshold	4	Mobs required before merging starts (see below)
merge.scanIntervalTicks	20	Ticks between merge scans — higher is cheaper
merge.maxMergesPerScan	64	Cap on merges per scan, to spread out the work
display.enabled	true	Show the count label at all
display.format	"%s ×%d"	Label format: mob name, then count
display.alwaysVisible	false	true shows the label without hovering
freeze.mode	"AGGRESSIVE"	AGGRESSIVE skips member ticks entirely; CONSERVATIVE only suppresses AI
entities.mode	"DENYLIST"	DENYLIST stacks everything except the list; ALLOWLIST stacks only the list
entities.denylist	villager, wandering trader, wither, ender dragon	Never stacked
entities.allowlist	empty	Used only in ALLOWLIST mode
safety.autoUnstackOnVersionChange	true	Unstack everything if the world was last opened on a different MC version
storage.virtualSpillThreshold	512	Reserved for phase 5; unused today

The crowd threshold

crowdThreshold is a gameplay feature, not a tuning knob: below it, nothing merges at all, so a couple of pet animals standing together never fuse. At the default of 4, merging starts at the fourth mob.

It counts true mob count, not entities — a neighbour that is already a stack of 3 counts as 3. So one 3-stack plus one loose cow reaches 4 and merges.

What never stacks

Beyond the denylist, a mob is left alone if it is named, leashed, tamed or ownable, riding or ridden, persistent, has no AI, is invulnerable, is a boss, is a baby, is in love, or is on a breeding cooldown. Every one of those represents either a deliberate player setup or a mechanic that would break if the mob were frozen.

Uninstalling

Delete the jar. Members are real entities the whole time, so they simply wake up on the next load — no migration step, no lost mobs.

For a clean exit, run /mobtimizer unstack all in each dimension first. That removes the mod's leftovers immediately rather than leaving frozen members to wake on their own.

Known issues

• Existing stacks made before 0.1.0 may contain babies. Fixed going forward, but calves already inside a stack stay there. /mobtimizer unstack all clears them.
• A stack loses one member per breeding pair. Expected — breeding needs two real animals. They rejoin after their cooldown.
• /mobtimizer stats says "1 stacks". Cosmetic.
• realisticallySpawnedZombiesWithRandomAttributeNoiseStillMerge is occasionally flaky, roughly 1 run in 4–10. A random spawn-time field on zombies is not yet in StackKeyFactory.IGNORED_KEYS; the same class of bug as the documented LeftHanded case. Affects the test suite, not gameplay.
• Untested with other mods that rewrite entity ticking. Lithium in particular is known to rewrite death and tick paths. HostPromotion deliberately uses Fabric's AFTER_DEATH event rather than a Mixin to reduce the risk, but this has not been verified under load.

Development

JAVA_HOME="/c/Program Files/Android/Android Studio/jbr" ./gradlew build

Runs 103 gametests against a real server plus the unit tests. Gametests share one level, so any level-wide assertion must be scoped by position or it will pick up other tests' entities.

Credits

Created and maintained by Aff55.

License

MIT. Copyright (c) 2026 Aff55.