Hi @Crudedragos and @rogermatic ! I am once again calling on your deep expertise. I have defined something like a dozen new creature types to try and balance different gameplay considerations with some atmospheric considerations. To that end, I have preserved the MONSTER type and added a SUPERNATURAL type. By default, the MONSTER spawn cap is set to 80 and the SUPERNATURAL spawn cap is set to 40. However, for some biomes, like my Netherlicious Abyssal Shadowland biome, I would like to invert that spawn cap, so that the SUPERNATURAL spawn cap is 80, and the MONSTER spawn cap is only 10. In the CreatureType.cfg file, I've defined these types as such:

    "MONSTER": {
      "Spawn Rate": 1,
      "Spawn Cap": 80,
      "Chunk Spawn Chance": 0.0,
      "Spawn Medium": "air",
      "Iterations Per Chunk": 3,
      "Iterations Per Pack": 4,
      "Spawn Tag": "obj.difficulty()==0||!solidside(1,{0,0,0},{0,-1,0})||liquid({0,0,0},{0,0,0})||normal({0,0,0},{0,0,0})||normal({0,0,0},{0,1,0})||!opaque({0,0,0},{0,-1,0})",
      "Default Biome Cap": -1,
      "Biome Caps": {
        "Abyssal Shadowland": 10
      }
    },
    "SUPERNATURAL": {
      "Spawn Rate": 1,
      "Spawn Cap": 40,
      "Chunk Spawn Chance": 0.0,
      "Spawn Medium": "air",
      "Iterations Per Chunk": 3,
      "Iterations Per Pack": 4,
      "Spawn Tag": "obj.difficulty()==0||!solidside(1,{0,0,0},{0,-1,0})||liquid({0,0,0},{0,0,0})||normal({0,0,0},{0,0,0})||normal({0,0,0},{0,1,0})||!opaque({0,0,0},{0,-1,0})",
      "Default Biome Cap": -1,
      "Biome Caps": {
        "Abyssal Shadowland": 80
      }
    }

This seems to be accepted as valid syntax by JAS. (I don't get a crash for invalid JSON, and I had previously noticed that my biome caps were deleted on loading the world because I accidentally typed "Abyssal Shadowlands", implying that JAS is checking that field for accuracy and accepting its current form.) However, in my Abyssal Shadowland biome, I run /jas composition and find that there are still 90+ monsters and only 45 supernatural creatures.

I could work around this by just merging the SUPERNATURAL type with the MONSTER type and tweaking the spawn weights for this biome accordingly, but I would like to be able to utilize this Biome Caps feature if possible. Do either of you know if I'm missing a step?