create-the-brass-oncerto/config/iceandfire/hippogryph_brown_biomes.json

{
  "biomes": [
    [
      {
        "type": "BIOME_TAG",
        "negate": false,
        "value": "minecraft:is_overworld"
      },
      {
        "type": "BIOME_TAG",
        "negate": false,
        "value": "forge:is_mountain"
      }
    ],
    [
      {
        "type": "BIOME_TAG",
        "negate": false,
        "value": "minecraft:is_overworld"
      },
      {
        "type": "BIOME_TAG",
        "negate": false,
        "value": "minecraft:is_hill"
      }
    ]
  ]
}