Is there any way we could make them spawn? One way would be to code a custom mob spawner algorithm, but this may be far to complicated.

Another way could be to make the biomes be a certain vanilla biome. You may create a custom jungle world with TC containing numerous different custom biomes but couldn't the biome data be the vanilla jungle? Is this possible now with the Anvil format?

I think better way is modify mobs arrays in BiomeBase, only one bad thing - default biomes will be changed in all worlds :/

But this things show me another potential BUG, now new worlds with TC save chunks with custom biomes ID.. need add options to choose this IDs

Some research:

The method BiomeBase.getMobs is returning one of these:
BiomeBase.J (monsters)
BiomeBase.K (Animals)
BiomeBase.L (WaterAnimals)

SpawnerCreature.a() Line #188 list is the mobs.
chunkPoviderGenerator.getChunkAt... uses world.getBiome() which returns a BiomeBase!
We pick a chunk using world.getChunkAtWorldCoords(i, j) chunk 810

I would like to fix this issue together with you Wickth. Preferably later today if you have time. I will be online 9h from now - I am in school right now :P We want ocelots for our rainforest at MassiveCraft but we do not really need NPC villages. So I would really want to fix this bug with you before we fix the other one :)

Ok, i will be in skype tonight :)

Ok I found one possible solution:
ce2be39

But yeah as you mentioned we save the chunks to disc (anvil) with custom biome ids embedded right? What if minecraft adds another biome? Are we reserving a lot of id's or did we... not think of this issue?

Ok it seems we did it :)