Mimic

Mimics were created as a lethal protection against looters. They are indistinguishable from normal chests until opened.

Detection
Using an Identify Scroll will let you know whether a chest is a mimic or not.

Combat
The fight against one mimic is a one enemy fight.

Mimics can steal from you.

Trivia
Mimics are probably a reference to mimics in other popular games, like Dark Souls or Terraria.