I'm currently playing Minecraft on a factions server where raiding is a pretty common occurrence. Obsidian is an effective defense against tnt and creepers, but a wither can still get through it. Would building my next obsidian base in a mushroom biome force enemy players to spawn a wither far away and lure it to my base, or can one be built in a mushroom biome?
Withers can be built anywhere. The only things to observe is that the last block cannot be placed in soul sand and that it cannot be assembled by pistons.