This mod lets you build a world out of only the biomes YOU want. It adds a new World Type called "Preferred Biomes". Open the list, check the biomes you want to see, leave the rest unchecked, and that's your world. Pick two, pick twenty, pick every cold biome and nothing else, whatever you're after. Modded biomes show up in the list too.
There's also an Island Survival Challenge option, which makes an ocean-only world dotted with islands, each one its own biome.
