Pumpkin/assets/datapack/data/minecraft/zombie_nautilus_variant/warm.json

{
  "asset_id": "minecraft:entity/nautilus/zombie_nautilus_coral",
  "model": "warm",
  "spawn_conditions": [
    {
      "condition": {
        "type": "minecraft:biome",
        "biomes": "#minecraft:spawns_coral_variant_zombie_nautilus"
      },
      "priority": 1
    }
  ]
}