Vicious Mushroom

These sprout on Crimson grass only, and the tile behind them has to be either bare or backed by the right kind of wall, which is why a tunnel you dug and walled yourself often refuses to grow any. Anything you swing takes one down in a single hit. Use a sickle instead and you pick up hay on top of the mushroom, which is free value if you are already sweeping a large patch.

There is one use and it is powder, either for spreading the Crimson into a farm biome or clearing it out of somewhere you want clean. You cannot eat them and no potion recipe wants them. They also sit outside the normal conversion chain, so you cannot flip a patch of ordinary mushrooms into these with powder or a solution the way the naming would suggest.