Mimics

A Mimic is a stealthy 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.

Mimics can be spawned by the player using the Chest Statue, even prior to Hardmode, 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.
 * The Spelunker Potion will not cause a Mimic to glow and the Hunter Potion will.
 * Mimics disguised as Gold Chests or Shadow Chests will not emit sparkles like the real versions do.
 * Hitting an inactive Mimic will activate it.
 * Mimics may not line up properly with blocks, as normal Chests would.
 * They can also appear in front of background objects, while real chests cannot.
 * They can also appear on spots where one of the blocks beneath it is an empty space, where real chests will never spawn.

Tips

 * Targeting Mimics may help players making their way through early Hardmode, and they drop high-damage weapons and good defensive accessories, as well as which will help with Hardmode's higher prices.
 * 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 a high place and attack 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.