Hammush

The mushrooms it throws off do land and do damage, but nothing about the swing makes this worth carrying as a weapon at the point you can buy it. What you are paying for is hammer power. It reshapes blocks and tears through background walls quickly, which matters when you are clearing out a large build, and like the Pwnhammer it breaks altars, so it works as a second altar smasher for a multiplayer world.

The Truffle needs a surface mushroom biome big enough to register and a house sitting inside it, which is a small building project on its own, and he will not open this line until a mechanical boss is down. If you were already growing that biome for the rest of his stock, the hammer comes along for the trip.

Both the name and the twin mushroom head come out of a long running Terraria fan comic, in which a character bolts two glowing mushrooms onto a handle years before the game shipped anything like it.