Vile Powder is a thrown consumable item that can be used to clear blocks of Hallow. It releases as a cloud spread with a very short range comparable to that of a Broadsword, and produces a fair amount of light when thrown. Vile Powder is the Corruption counterpart to Purification Powder. It can be crafted from Vile Mushrooms, or purchased from the Dryad during a Blood Moon. It does indeed have a counterpart for The Crimson; the Vicious Powder.
Vile Powder returns Pearlstone to Stone, Pearlsand to Sand and Hallowed grass to normal grass. It can also be thrown at a Bunny to transform it into a Corrupt Bunny, at a Goldfish to transform it into a Corrupt Goldfish, or at a Penguin to transform it into a Corrupt Penguin.