Toxic Sludge

The Toxic Sludge is a Hardmode slime enemy that appears in the Underground layer in place of normal slime enemies. They deal a vastly increased damage from normal slimes, and they also have a 50% chance on hit to afflict the player with Poison. They drop gel like the other slimes.

Trivia

 * Toxic Sludges bear notable resemblance to numerous creatures from video games and other media, including Blargg and similar enemies from Yoshi's Island, and Muk, known as "the sludge Pokémon," from the Pokémon franchise.
 * Toxic Sludge and Pinky are the only two members of the Slime family not to have the word "slime" in their name.