Mimics

A Mimic is an uncommon Hardmode enemy disguised as a Chest, appearing as the appropriate Chest type for the environment. Mimics can be spawned by the player using the Chest Statue, even prior to Hardmode, but these do not drop any coins or items besides the Mimic Banner.

Normal
Normal mimics look exactly like Chests until approached or attacked, at which point they will chase the player. They take on the appearance of chests normally found in that biome: regular chests above the Underground layer, gold chests Underground, and locked Shadow Chests in The Underworld. Mimics that spawn in a Snow Biome take the appearance of Ice Chests, and also have their own unique set of ice-themed drops.

Special variants
Four Mimic variants have much higher health, more advanced attacks, and separate sets of unique drops. Similar to ordinary Mimics, they will disguise themselves as Chests until attacked or approached, but once they reveal themselves they do not resemble any Chest type currently in the game.

Each of the four have the same attack method. Similar to ordinary Mimics, they can attack by jumping towards the player, but they also have the ability to shut themselves, making themselves invincible. In the closed, invincible state, these mimics are capable of reflecting player projectiles; reflected projectiles can result in damage to players. They can also perform a pound-like attack, where the Mimic jumps over the player's head and swiftly drops down; during this attack they can move through blocks. They can additionally dash rapidly after the player at high speeds if the player attempts to escape, and can sometimes dash through blocks.

The Corrupt, Crimson and Hallowed Mimics can be difficult in early hard mode, especially in expert mode due to their speed, high health and high damage. However, if a player has obtained a Blessed Apple, they can be outrun and defeated easily by attacking with any ranged weapon.

In addition to natural spawns, the Hallowed Mimic can be spawned by placing a Key of Light in an empty chest, and the Corrupt Mimic or Crimson Mimic can be spawned with the Key of Night.

Jungle Mimics are currently unimplemented, and do not spawn naturally and they can't be spawned manually with an item.

Identification
While disguised, Mimics will not show a usual enemy tooltip when hovering the mouse cursor over them, except in the mobile version. 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, but the Hunter Potion will. The Spelunker buff will give it a yellowish tinge, and the Hunter Potion will make it bright red.
 * Mimics disguised as Gold Chests or Shadow Chests will not sparkle, as opposed to real chests.
 * Hitting a disguised Mimic with any weapon, including ranged weapons, homing weapons, and Minions, will activate it.
 * Mimics may not line up properly with blocks, as normal Chests would. They can also spawn halfway inside blocks, and in front of background objects and enemies, where real chests can't be placed. They can also spawn on the edge of a block, rendering it floating and confirming it a mimic.
 * Mimics cannot disguise themselves as unlocked Shadow Chests. Unlocked Shadow Chests are always real chests. Similarly, they cannot disguise themselves as locked Gold Chests, which appear in the Dungeon
 * The Lifeform Analyzer will detect nearby Mimics. The Metal Detector can also give them away, as there will be no "Nearby Chest detected" message.
 * If the mimic spawns while standing in lava it will take damage from the lava every tick even while it is not yet attacking the player.
 * Removing all the naturally spawned chests underground prior to hardmode, while tedious, will guarantee that any chests seen in the future are mimics.
 * Any Gold Chest found outside of Underground Cabins in maps made in the 1.3 version is guaranteed to be a Mimic. Golden Chests are not naturally spawned outside of Underground Cabins anymore.
 * Hallowed, Crimson, and Corrupt Mimics are much larger than normal chests, and have no lootable counterparts (i.e. a gold chest can be a mimic or an actual chest, but a hallowed "chest" can only be a mimic). The Biome Chests in the Dungeon have a different appearance to mimics.
 * Mimics are affected differently by light.

Tips

 * Targeting Mimics can help players making their way through early Hardmode, as they drop high-damage weapons and good defensive accessories, as well as around, which can help with Hardmode's higher prices.
 * An easy way to kill Mimics early in Hardmode is to grapple a high place and attack with a ranged weapon. However, early Hardmode players should beware of Hallowed and Corrupt/Crimson Mimics since the mentioned tactics won't work against them because of their abilities to jump to almost any location and pass through blocks.
 * Key of Light/Night spawned Hallowed and Corrupt/Crimson Mimics however can still be easily defeated using a similar tactic to the above on the surface - using a platform very high in the air such that the mimics can barely reach you will cause them to jump up constantly from the surface below (which will be a little off screen) in such a way that they are very easy to dodge with minimal movement and can be attacked with any weapon whenever they jump up.
 * With 3 or more players, Mimics will never stay in their disguised state.
 * A way to hunt down mimics is to have the Lifeform Analyzer in your inventory, and look for chests in locations which a chest would not normally be able to be placed, i.e. on one normal block and one sloped block.

Trivia

 * Mimics first appeared in Dungeons & Dragons in 1977, and have appeared in countless publications since.
 * In the mobile version, Mimics are ridiculously easy to identify since they will always have the enemy indicator over them.

History
Mimic