Maybe this is already in, or can be added by 0.35's ability to craft new attack methods, but how about invisibility? Some sort of "Cape of Cloaking" that can cast the spell. (Or, hey, a cloaking device, if there's a sci-fi dungeon, like has been thrown about a few times)
As a bit more out there, maybe monsters can use it too, and then they are displayed as their transparent versions when they're one space away, and not drawn otherwise.
Hmm... cloaked Vexirks
EDIT: Yes, I know they're all wearing cloaks. That's not what I meant
