There were other variants including SPACE MIMICS (prefers to mimic a desk, incidentally). There's also the Elder Mimic, which mimics a room instead of an entire house.
3rd edition removed nearly all of the variants, though they have some systematized rules for 'advancing' a Mimic's size. There is an epic relative of the Mimic though, the Genius Loci, which mimics an entire section of the landscape instead of just a building.
I don't know how people in the D&D world survive day by day. Literally everything is trying to kill you!
No kiddin'. Even some of the magic items want to kill you (part of the same reblog chain as my previous link, no less)! One thing technically qualifies as both a disguised creature that wants to eat you and a seemingly-helpful magic item that actually wants to kill you. As the original poster implies, it wouldn't take too much effort to do an SCP Foundation-esque setting in D&D (or its D20 Modern offshoot).
