On Fire!

On Fire! is a debuff which prevents regeneration and causes the afflicted NPC or player to lose 4 health per second. When an enemy is, it will lose 29 health per second instead.

The debuff can be canceled by jumping into water, or by pouring a Water Bucket over the player's head. The Obsidian Skin Potion also grants immunity to this debuff for the duration of its effect. Molten armor provides immunity to the debuff while worn.

Trivia

 * The debuff icon appears to depict the Guide Voodoo Doll.
 * It is the only debuff which has exclamation mark in its name. The Happy!, Panic! and Ballista Panic! have exclamation marks on their names as well, but they are buffs rather than debuffs.