D&D knows Mimics and their relatives, the Lurker and Trapper. They are aberrations that mimicpun intended the floor and ceiling and have been used in conjunction with a stunjelly for years to make a room that lusts for adventurers to eat. Yes, the room will eat you. For example in this 2010 Screamsheet blog post describes "The Room of Death" with many more monsters for Pathfinder, but I was very sure I have seen an older internet page that discussed the two aberrations with the stunjelly in an empty room configuration. After a quick search I could find where I had read it first: Jared [von] Hindman's 2006 article ranting about 30 years of stupid monsters includes the (empty) Room of Death but labeled it as "Trinity of Dungeon Terror".1
Other terms for such a setup I have seen or heard in discussions are Living Room, Killer Room and Room of Doom.
Has there ever been a pre-2006, official Dungeons and Dragons supplement, or Dragon Magazine article that employed the idea of the killer room that wants to eat you, consisting of 3 different monsters that make up the ceiling, wall and floor? The most iconic combination seems to be Lurker, Trapper and Stunjelly but the first mention might have used other monsters.2
1 In fact, I used his articles to build a house filled with monsters that imitate items to try to eat you but that's beside the point.
2 A single Greater Mimics doesn't count. Neither does a House Hunter Mimic or a set of 3 mimics. It must be 3 monsters with different stats making up the ceiling, floor and walls.