Lair of the Hardcore Dangerous Extradimensional Sorcerer

A high-level dungeon, season to taste.The PCs are nominally supposed to free the prisoner (8) and defeat the Sorcerer (21).The entire dungeon is made of some material on the border between crystal and white marble with translucent veins that seem to move. The material automatically resists any attempt to manipulate or bypass it--it has an extra saving throw to prevent Passwall, Stone Shape, Teleportation, et al. and if that save succeeds, some unsavory disaster will occur--the caster ends up half-stuck in the wall, for instance.1.Eldritch PolyhedraThese are hovering guard constructs, each about the size of a fridge. They cast a random offensive spell at any intruder every round as if 10th level. AC 20, 50 hit points.2.Perfidious MirrorEntering the room through either of the trapped doors without the Sorcerer's key activates the mirror. It reflects everything accurately except it also contains a thief, who pickpockets one (real) item per round the room is occupied by stealing it from…