Living Wall
The Living Wall is easily the most horrific thing that came out of Dungeons & Dragons 2nd Edition. If it had come out in 1e it still would have been deemed Edge.
What it is, is the backdrop to Palpatine's digs in Revenge of the Sith - or, better, those lost souls trapped in resin in Aliens. It's a coagulated mess of every human or other sentient that the wall ever consumed. The trapped souls in this wall aren't quite dead, yet - and they'll call for you to pull them out of the slurry.
Don't. Seriously: don't.
When you lose your battle against the Living Wall, you become a part of it and you are assimilated to it. This adds to its power to the point that it retains the spells of assimilated magic-users. And you're not getting out save by a wish cast from the outside and, you know how those usually work.
The Living Wall started in Ravenloft whence it got promoted to the 1993 Monstrous Manual. It got out to other horror-themed modules like Gates of Firestorm Peak. (There's a "living wall" in the Fiend Factory but that became the Stunjelly, it's not related in the slightest.)
Lorraine Williams had promised her 2e players they'd be getting the nerfed, "child friendly" edition without all those demons and junk. And they got this. Good job, Lorraine; thanks for the nightmares.
