Mimics

A Mimic is an aggressive Hardmode enemy disguised as a Chest, appearing as the appropriate Chest type for the environment. Mimics will look exactly like Chests until approached, at which point they will chase the player.

Mimics take on the appearance of Chests that would normally be found in a given area: normal brown chests closer to the surface, gold chests found underground, and locked Shadow chests in The Underworld.

Mimics that spawn in a Snow biome not only take the appearance of Ice Chests, but also produce their own unique drops (see the lower infobox).

Mimics can be spawned by the player using the Chest Statue, but they will not drop any coins or items besides the Mimic Banner.

Identifying
While disguised, Mimics will not show a usual enemy tooltip when hovering the mouse cursor over them. Below are some tips to help differentiate real chests from Mimics.
 * Real Chests will show up on the minimap, but mimics will not.
 * Spelunker Potion will not cause a Mimic to glow, and Hunter Potion will.
 * Mimics disguised as Gold Chests or Shadow Chests will not produce a sparkle animation as the real versions do.
 * Hitting an inactive Mimic will activate it.
 * Mimics may not line up perfectly with blocks, as normal Chests would.
 * They can also appear in front of background objects, which real chests cannot.

Tips

 * Mimics are much easier to beat on flat land with high tier Spears.
 * An easy way to kill Mimics early in Hardmode is to grapple to a high place and attack the Mimic with a ranged weapon.
 * On the Console version, with 3 or more people on, mimics will never stay in their hidden "Mimic" state, thus making it easier to make a farm and less risky to attack.

Trivia

 * Mimics first appeared in Dungeons & Dragons in 1977, and have appeared in countless RPGs since.