Mimic

Hardmode is the usual gate, and the disguise copies whatever container belongs to the area you are in: plain wood above ground, gold through the underground and caverns, locked shadow chests down in the Underworld, and frozen ones in the snow, which come with their own ice themed loot. Wooden ones on the surface need unexcavated dirt wall behind them, and that is also the cheapest farm for the common kind: level a stretch of ground so a wide face of natural dirt wall is exposed and they appear there faster than they do in caves. A Chest Statue makes them at any stage of the game, before Hardmode included, but statue spawns pay out nothing except the banner. Two of the special world seeds let weakened pre-Hardmode versions with different loot appear underground.

You identify them by what is missing, not what is there. Real containers appear on the minimap and these do not. With smart cursor turned on, a genuine chest gets a yellow outline as you approach and a fake one never does. Gold, frozen and shadow chests give off an animated sparkle, and the copies of those three do not, which is the fastest read available. That tell is useless on wood, since real wooden chests do not sparkle either.

A Spelunker Potion highlights containers only while a Hunter Potion tints enemies, so running both sorts a room instantly, and a Lifeform Analyzer simply names them. Failing that, look at placement: they often sit off the tile grid, half buried in a block, or hanging over a ledge where the real thing could never be placed. Any hit wakes one, including a stray minion or homing shot, and lava sets off a disguised one too.

An ordinary mimic carries one of the biggest coin drops in the game outside of bosses, which matters because early Hardmode reforging and potion costs are ugly. Inflicting Midas multiplies the payout, and Golden Bullet ammo or a Flask of Gold both do that. They also jump poorly, so a Rope, a ledge or a grapple keeps you clean out of reach while you shoot down at one. Battle Potions and Water Candles push the spawn rate as they would for anything else, and the jungle underground is well worth camping in.

The special versions haunt the underground stretch of their matching biome and are far bigger than any real container. You can also make one on purpose: put a single Key of Light into an otherwise empty chest, or a Key of Night for the evil version, then close it. Whichever evil your world generated with decides which one the night key produces, except in a drunk world, where it rotates daily. The jungle variant is the odd one out, existing only under the Celebration Mk 10 seed with no way to summon it by hand, which is why it has no bestiary entry either.

Only one of each type can be alive at a time, and every type currently eligible to spawn cuts the chance of ordinary mimics in half, in a fixed priority order. Standing where several biomes overlap skews the results heavily.

Three hops in your direction, then one of three moves, then back to hopping. It can chain fast dashes with a jump height no chest should have. It can shut itself and go completely untouchable, and in Expert that closed state throws your own bullets, arrows and darts back at you. Rockets and a long list of other projectiles are not reflected, but a single heavy shot from something like a Sniper Rifle coming back at you can end the fight on the spot, so save the big single hits for when it is open. The third move is a pound: it leaps over you and comes down through anything in the way, terrain included. Try to run and it dashes after you faster than early Hardmode wings will carry you, again through blocks, so the rope trick that trivializes a common mimic does nothing here.

Fight them somewhere open. A big cave or a flat arena with room to move sideways is worth more than any amount of defense. Wings handle the pounce. A straight line handles the dash, since a hellevator, a minecart track or a fast mount on level ground keeps you permanently just ahead of it while you shoot back. The jungle one adds a move nobody else has, flinging a handful of loose blocks at you.

Corrupt and Crimson drops pull in opposite directions, which is worth weighing when you create the world. The corrupt kit is built for fighting at range: a flail with heavy knockback, a wall of flame to hold ground, and an accessory that makes enemies lose interest while paying you damage for it. The crimson kit assumes you are up close: one of the shortest melee weapons in the game, something that returns health as you swing, and an accessory that pulls aggro onto you and hands back defense to survive it. Hallowed covers the weapon classes but has no accessory equivalent. If you want the other side's gear, buy the opposing evil's seeds from the Dryad once she is standing in a Hardmode graveyard, then grow an artificial biome underground.

They also hand over Greater Healing Potions and their mana equivalent, useful in the window before you can brew your own. The jungle variant is the exception: its drop list is a joke, so nobody farms it twice.

• Biome mimics hit like bosses without being bosses. No boss health bar, banners instead of trophies, and no relic in Master.
• A bridge left over from the Wall of Flesh fight doubles as a patrol route with the analyzer in your bag.
• They need fewer kills than most enemies to finish the bestiary entry and unlock the banner.
• They cannot imitate an unlocked shadow chest or a locked gold chest in the Dungeon, so those two are always genuine.
• Carry the analyzer while mining near the underground evil or Hallow early in Hardmode. Meeting one of these by accident in a tunnel is how runs end.