For those with pointy eared hopes
The way the Nameless One is described heavily implies a connection to the Sleeping Serpent. Black scales, golden claws, matches with the dragon/yuan-ti boss description in Morgan's arc. Also Pyramids were heavily featured in that arc as well. Unless Adam has a real hard on for that particular color scheme (who knows?), I'd say that this connection was on purpose. Kalimat probably just woke a sleeping dark god, or at least got him a lot closer. Perhaps this where it's physical form (or a part of it) slumbered.
Black Dragon vs Necromancer King showdown in the Valley? Throw in some fire elementals for a good time.
The scarab card does harken more toward the elves, however it does not match the Nameless One (and if the Ki-rin does not know about this prisoner I doubt the Gith do). If we go with the disguise/illusion theory how can you trust the cards? If we can't trust Kalimat's senses here at least every visual clue is in doubt.
Also shame on you Adam calling it the Oubliette without the door being on top of the cell. #TrapdoorGate