Board Thread:Questions and Answers/@comment-71.223.191.40-20121228162820/@comment-5584420-20121229023815

Okay, since you said it changes the biome,do this to verify is it 'real' mushroom biome

Dont place any light and wait from ~32 blocks away, if its real mushroom biome, it will not spawn.

Btw, how big is the area? might be ur too close to the biome for mobs to spawn, some steps that (maybe) will increase mooshroom chance

1. The most important,go within ~32 blocks away, mobs cant spawn too close to you

2. KILL ALL the passive animal you seen,they are pushing the mob limit

3. Light up the area(MushroomBiome), at least monster wont kill you while waiting for mushroom, and make all other area dark (so normal animal cant spawn outside the mushroom biome)