MicroMobs — Realistic Mob Sizes

A Fabric mod for Minecraft 1.21.11 that rescales mobs to closer real-world biological proportions.

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Scaling at a glance

Category	Examples	Scale
Tiny insects	Silverfish, Endermite	10 %
Small insects	Bee	18 %
Small arthropods	Cave Spider, Spider	22 – 25 %
Small aquatic	Pufferfish, Tadpole	20 – 40 %
Amphibians	Frog	35 %
Small animals	Rabbit, Parrot, Fox, Cat	60 – 75 %
Medium animals	Pig, Sheep, Wolf, Cow	90 – 95 %
Aquatic	Cod, Salmon, Turtle, Squid	80 – 95 %
Slime / Magma Cube	Base size −30 %	70 %
Large / Bosses	Iron Golem, Warden, Ender Dragon	100 % (unchanged)
Monsters	Zombie, Skeleton, Creeper, Enderman…	100 % (unchanged)

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Features

• SCALE attribute — scales model, hitbox, eye-height and shadow in one shot using Minecraft's built-in attribute system (no render hacks).
• Speed boost for tiny mobs — Spider ×1.2, Bee ×1.15, Silverfish & Endermite ×1.3.
• Higher pitch sounds — Bee, Silverfish, Endermite play at elevated pitch.
• Persistent modifiers — stored in NBT so the modifier is only written once per entity, even across world reloads.
• JSON config — every scale is tuneable via config/micromobs.json.

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Requirements

Dependency	Version
Java (JDK)	21+ (or any JDK — toolchain auto-provisions 21)
Minecraft	1.21.11
Fabric Loader	0.18.4
Fabric API	0.141.3+1.21.11
Gradle wrapper	9.2.1 (auto-downloaded)
Fabric Loom	1.15.5

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Building

Quick local testing environment (recommended)

From the project root, run:

cd "D:\\Slimeey Studios\\actual size"
Set-ExecutionPolicy -Scope Process Bypass -Force
.\\test-client.ps1 -PrepOnly

This pre-downloads assets, prepares Loom launch files, and generates IDEA sync data. Then launch the dev client with:

.\\gradlew.bat runClient

1 - Prerequisites

Install Java 21 JDK and make sure JAVA_HOME points to it:

$env:JAVA_HOME = "C:\path\to\jdk-21"
java -version   # should print 21.x.x

2 — Wrapper / setup

The Gradle wrapper is already included in the repository, so in most cases you can build immediately.

If you ever need to re-download or repair the wrapper locally, run:

cd "D:\\Slimeey Studios\\actual size"
.\setup.ps1

3 — Build

.\gradlew.bat build

The first build downloads Minecraft assets and yarn mappings (~500 MB). Subsequent builds are fast.

The compiled JAR will be at:

build\libs\micromobs-1.0.0.jar

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Installation

1. Install Fabric Loader 0.18.4+ for Minecraft 1.21.11.
2. Install Fabric API for 1.21.11.
3. Drop micromobs-1.0.0.jar into your .minecraft/mods/ folder.
4. Launch Minecraft 1.21.11 with the Fabric profile.

On first launch the config file is written to:

.minecraft/config/micromobs.json

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Configuration

Edit config/micromobs.json while the game is closed:

{
  "spiderScale": 0.25,
  "caveSpiderScale": 0.22,
  "beeScale": 0.18,
  "silverfishScale": 0.10,
  "endermiteScale": 0.10,
  "frogScale": 0.35,
  "tadpoleScale": 0.20,
  "chickenScale": 0.75,
  "rabbitScale": 0.60,
  "foxScale": 0.70,
  "catScale": 0.70,
  "ocelotScale": 0.70,
  "parrotScale": 0.65,
  "pigScale": 0.90,
  "sheepScale": 0.90,
  "cowScale": 0.95,
  "goatScale": 0.90,
  "wolfScale": 0.90,
  "pandaScale": 0.95,
  "codScale": 0.80,
  "salmonScale": 0.90,
  "pufferfishScale": 0.40,
  "tropicalFishScale": 0.70,
  "squidScale": 0.80,
  "glowSquidScale": 0.80,
  "axolotlScale": 0.50,
  "turtleScale": 0.80,
  "dolphinScale": 0.95,
  "slimeScale": 0.70,
  "magmaCubeScale": 0.70,
  "enableMovementAdjustments": true,
  "enableSoundAdjustments": true
}

Set enableMovementAdjustments to false to disable the speed boost for tiny mobs. Set enableSoundAdjustments to false to keep vanilla sound pitch.

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Technical notes

Why SCALE?

SCALE (added in Minecraft 1.20.5) is the official attribute for proportional entity scaling. Setting it to 0.25 scales the entire entity — hitbox, eye-height, shadow, renderer — in one attribute write. No per-tick code, no render injection required.

Modifier lifetime

addPersistentModifier() saves the modifier in the entity's NBT tag. The ENTITY_LOAD listener checks whether the modifier is already present before writing, so the scale is applied exactly once per entity — whether the mob spawned naturally, from a spawner, via command, or by spawn egg.

Slimes & Magma Cubes

These mobs scale their dimensions dynamically based on their "size" tag (1, 2, 4). Applying SCALE = 0.70 uniformly reduces every size tier by 30 %, so a large slime becomes 70 % of its vanilla large size, etc.

Sound pitch

The mixin injects at the RETURN point of LivingEntity.getSoundPitch() and multiplies the returned value. All ambient, hurt, and death sounds for the entity route through this single method, so one injection covers everything. The injection uses require = 0 — if the method signature ever changes in a future Yarn build the mixin silently no-ops rather than crashing.

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Troubleshooting

Symptom	Fix
Attribute SCALE not found	Update to Minecraft 1.21.11; SCALE requires >= 1.20.5
EntityAttributeModifier.Operation.ADD_VALUE not found	You are on a pre-1.20.5 mapping; use ADD instead
Wrapper JAR missing	Run ./setup.ps1 or regenerate the wrapper locally
Sound mixin fails silently	Normal behaviour — require = 0 means an incompatible method signature just disables the pitch injection
Mob still vanilla size after installing	The mod requires Fabric API on the mods list; double-check it is present

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Project structure

.
├── build.gradle
├── gradle.properties
├── settings.gradle
├── gradlew.bat
├── LICENSE
├── README.md
├── gradle/wrapper/
│   ├── gradle-wrapper.jar
│   └── gradle-wrapper.properties
├── setup.ps1
├── test-client.ps1
└── src/main/
    ├── java/com/slimeey/micromobs/
    │   ├── MicroMobs.java            ← mod entrypoint
    │   ├── MicroMobsConfig.java      ← JSON config loader / saver
    │   ├── MobScaleManager.java      ← scale table + event registration
    │   └── mixin/
    │       └── LivingEntitySoundMixin.java  ← pitch adjustment
    └── resources/
        ├── fabric.mod.json
        ├── micromobs.mixins.json
        └── pack.mcmeta