This rare biome consists of a mixture of flat landscape and steep hills and has mycelium instead of grass as its surface. However, if you do place down grass, it is a very bright green color, not unlike that of the Jungle biome. Mushroom islands are always adjacent to an ocean and is often found isolated from other biomes. It is the one of two biomes where huge mushrooms can spawn naturally (the other being the roofed forest biome), and where mushrooms can grow in full sunlight.
No mobs other than Mooshrooms spawn naturally in this biome, including the usual night-time hostile mobs. This also applies to caves, abandoned mine shafts, and other structures underground, meaning exploring underground is relatively safe. However, monster spawners will still spawn mobs, and the player will still be able to breed animals and spawn mobs using items.
Trees can be grown from saplings in this biome, as well as other dirt or grass-based plants, as long as they are not directly adjacent to mycelium, which will take over the dirt square from the plant and uproot it. Mycelium cannot be tilled directly, but it can be dug away and replaced as dirt, then immediately tilled. Once created, farmland can resist takeover by mycelium.