The Mimic is a monster invented by Dungeons & Dragons and which has become famous throughout /tg/ and beyond. In contrast to its close kin, the Rust Monster and the owlbear, the Mimic is not remembered for being a goofy idea, but for its sheer deadliness, which has seen it readily adapted in /v/ media.
The mimic has its roots in Old School Roleplaying, most specifically the tendency for such games to boil down to a sadistic DM out for blood vs. a bunch of paranoid players. Something like a slime with a hard shell instead of a gelatinous membrane, the mimic is an amorphous predator that disguises itself as inanimate objects in order to lure potential meals close, then attack. Most iconically, they take the form of treasure chests, making them one of the most recognizable of "gotcha!" monsters.
To further the paranoia, the mimic has often been portrayed as having more advanced shapeshifting than that; Advanced Dungeons & Dragons gives them the Greater Mimic (big enough to pretend to be entire rooms) and the Househunter Mimic (big enough to pretend to be whole houses), third edition (and Pathfinder) include notes that mimics increase in size if advanced in hit die, whilst 4th edition states that in their adult forms, mimics can disguise themselves as human beings and walk amongst them to find prey.
What few except real grognards remember is that, originally, the AD&D mimic came in two forms; the regular mimic, whilst still a hungry predator, was quite intelligent. With a Int rating of 8-10, it was about as smart as your average human being, capable of speech, and more than willing to bargain in exchange for food (and not that fussy; enemy corpses, spare trail rations, they'll eat it). The more iconic modern depiction of the mimic comes from the variety AD&D labeled the Killer Mimic, identical in every way except that it was tougher and far stupider (Int 2-4, so only animal intelligence), meaning it just attacked whatever food it could find.
The connection between Househunter Mimics and the Gazebo meme remains unclear.
Mimics as Monstergirls
|This article or section is about Monstergirls (or a monster that is frequently depicted as a Monstergirl), something that /tg/ widely considers to be the purest form of awesome. Expect PROMOTIONS! and /d/elight in equal measure, often with drawfaggotry or writefaggotry to match.|
Like many iconic D&D monsters, the Mimic has a Monstergirl version. Same general idea of a shapeshifting creature camouflaging as a treasure chest, except the 'inside' of the box looks like a pretty girl often depicted wearing the traditional Shinto shrine maiden uniform of white blouse and red skirt (due to the phonetic resemblance and obvious tongue-in-cheek of the second syllable of the English word "mimic" and the Japanese term "巫女" (miko) for shrine maiden) out to have some fun with any unwary adventurer she catches.
If the adventurer is lucky, that is. Let us just say that the Mimic is just as often used to sate much darker and disturbing fetishes and leave it at that...