Toxic Sludge

The Toxic Sludge is a Hardmode Slime Enemy that appears in the Underground in place of ordinary Slimes. They deal significantly increased damage and have a 50% chance of inflicting the Poisoned Debuff, which they are also immune to. They also happen to be the cutest type of slime in the game, period.

Trivia

 * The Toxic Sludge is one of the few enemies in Terraria to have a visible smile, the others being the Clown, Snow Balla and Snowman Gangsta.
 * Disregarding the Gastropod, it is the only slime on which a face is visible.
 * The Toxic Sludge seems to be an adult version of the Baby Slime summoned by the Slime Staff, given its similar colors and face.

History
毒泥 Токсичная муть Gadoue toxique