For some reason, when generating my biome, none of the mobs that I put in there will ever spawn, though sometimes default vanilla animals I haven't added will. I've tried generating my biome in a single biome world and the mobs I desired spawned but it needs to work for a default world preset.

This is the json file for my biome: https://gist.github.com/Phoenix-WB/e6499a5e5e660d5d4435262f32e61e41

We can't tell you what is wrong from one random configuration file. We need to know how you are using it.

 

But just creating a biome does not add it to the default world generation, that has a hardcoded list of biomes.

If you want to add biomes to vanilla worldgen, you need to use a mod like: https://www.curseforge.com/minecraft/mc-mods/terrablender

 

I forgot to mention that I am using terrablender, but yes I am, and I've been following this example from them here: https://github.com/Glitchfiend/TerraBlender/tree/TB-1.19.3-2.1.x/Example/Forge

Would you need any other specific files from that for diagnosis?

If you have issues with terrablender, you need to speak to them.

Supposedly it's not a terrablender issue according to them so idk ¯\_(ツ)_/¯