Some of you may know that I am Bone's brother. If you didn't you do now. I did some research and testing with the Mycelium. With the Silk Touch enchantment the Mycelium can be picked up. It will spread to other dirt blocks. It will not spread onto dirt blocks that have grass on them. Mooshrooms do not spawn on Mycelium. They only spawn in mushroom biomes. Outside the mushroom biomes Mycelium acts just like grass. All mobs will spawn on it except Mooshrooms, Silverfish, and Cave Spiders. The only bonus is that mushrooms can be on it in every light level. I don't know if Bonemeal works on it or what it does.
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Thanks,
Jailbird556.