Mobs Data Packs

What a mob data pack can change

A data pack cannot add a new kind of mob. Entity types are built into the game, so packs that seem to add one take an existing mob and change it with commands, attributes and usually a resource pack for the looks. What a pack can change directly is still a lot: drops through loot tables, which mobs a biome spawns, and the textures and spawn conditions of variants such as cats, chickens and cows.

Larger Phantoms

Phantoms only appear above a player who has gone at least three in-game days without sleeping, and every phantom that spawns naturally is size 0. The size can go up to 64 and a phantom deals 6 damage plus its size, so a phantom that grows also hits harder.

Silence Mobs

Vanilla already reacts to a few names: Dinnerbone or Grumm turns a mob upside down, jeb_ makes a sheep fade through the dye colors and Toast gives a rabbit its own skin. Those names are case sensitive. A pack like this one adds its own name trigger on top.

Drops and the player kill rule

Every mob has its own loot table, and the phantom's is one of the shortest in Java 26.2: a single pool with the killed_by_player condition that gives 0 or 1 membrane, plus up to 1 more per level of Looting. The condition only passes when a player hurt the mob shortly before it died, so a phantom that burns up in the morning sun without a player hitting it drops nothing. Wither skeleton skulls follow the same rule and drop 2.5% of the time, 3.5% with Looting I and another 1% for each level above that.

Experience is not part of any loot table. The game code decides how much a mob gives, so a pack that hands out more has to do it with commands, for example by summoning experience orbs from a function. The ender dragon shows the split well: its loot table in 26.2 is empty, and its experience and the egg come from the fight itself.

Spawn weights and mob caps

Natural spawns come from the spawners list in each biome file, where every mob has a weight and a group size. A weight is only compared with the other entries of the same category in that biome, so one mob can be rare in one place and common in the next. In 26.2 a panda has weight 1 in a jungle and 80 in a bamboo jungle, while parrots sit at 40 in both. Mushroom fields and the deep dark have no monster entries at all. Phantoms, wardens, patrols and the cats in villages don't use these lists; they spawn by their own rules.

How many mobs spawn is set in the game code, not in a data file. Java counts the loaded mobs of each category against a cap: 70 monsters, 10 creatures (the land animals), 15 ambient mobs (bats), 5 axolotls, 5 underground water creatures such as glow squid, 5 water creatures and 20 water ambient mobs (fish). With one player those are the real numbers, and with more players the cap grows with the loaded chunks around them. A pack that raises a weight changes which mob turns up, never how many. Spawners, breeding, spawn eggs and /summon ignore the caps completely.

Some changes need no pack at all. Java 26.2 has separate game rules for spawn_phantoms, spawn_monsters, spawn_patrols and spawn_wardens, and spawn_mobs switches off natural spawning as a whole.

Variants live in data files

Wolves went from one look to nine in Java 1.20.5, and 1.21.5 split cows, pigs and chickens into temperate, warm and cold. Every variant is a file with its own spawn conditions, so a pack can move one to other biomes without touching the mob. In 26.2 the warm farm animals use the biome tag #minecraft:spawns_warm_variant_farm_animals, which holds the desert, jungles, savannas, badlands, the mangrove swamp, warm and lukewarm oceans and the Nether. The cold tag holds the snowy and frozen biomes along with groves, jagged and stony peaks, every taiga, the windswept hills and forest, cold oceans, the deep dark and the End. Anywhere else you get the temperate version.

Wolves have one biome each: woods in forests, ashen in snowy taigas, black in old growth pine taigas, chestnut in old growth spruce taigas, snowy in groves, rusty in jungles, spotted in savannas, striped in badlands and pale wherever none of those apply. Cats pick their coat at random, with one exception: the all black cat is the only one a swamp hut spawns, and anywhere else it only joins the draw on a full moon.

Names, silence and despawning

Every entity has a Silent flag, so muting a single mob needs no pack: /data merge entity @e[type=cow,limit=1,sort=nearest] {Silent:1b} silences the nearest cow and {Silent:0b} brings the sound back. A pack with a name trigger saves you the typing. Mobs also have a NoAI flag that stops them from moving on their own, which is handy for a display.

A name tag has a side effect that matters for farms: most named mobs never despawn, with wandering traders and hostile mobs on Peaceful as the exceptions. In Java a name can be 50 characters long and costs 1 level to write on an anvil. A mob that can despawn at all disappears the moment no player is within 128 blocks. Beyond 32 blocks it gets a 1 in 800 chance every tick once it has been out of range for 30 seconds, or 10 seconds for a monster in light above 12, which works out to about 2.5% a second.

Installing one

Put the zip in the datapacks folder inside your world, run /reload and check that it is on with /datapack list enabled. New drops only apply to mobs that die after that. A pack that changes biomes, and with them the spawn lists, needs the world reopened or the server restarted instead, because /reload does not pick up those files. When two packs replace the same file, the pack loaded last wins; disable one and enable it again with /datapack enable <name> last to move it to the end.