Minecraft wiki entry for Achievement_guide, associated text: Find a cow, mooshroom, horse, donkey, or a llama. Cows can appear at any place with grass and enough light, unless it is an ocean biome. Horses and Donkeys can only spawn in a plains and savanna biome. Red mooshroom only spawn in mushroom fields biome. Llamas only spawn in mountains and savanna biomes. You may have to wander a bit to find one, so make sure you'll be able to find your way back.