We played again and have another session tomorrow.
1) Continual Flame torches are everywhere, and they're worth 50gp each! The greedy wizard is getting very excited about all the loot (I've been very stingy in general, so this is a windfall)
2) How does the water drain from area D9 when it's 50' below sea level? Magic suction pumps? And why would anyone go to such measures? It feels so random. I guess it hides the entrance really well? It also keeps out gaseous form creatures, as my PCs realized.
3) Where are the drain openings? More importantly, where is the opening for the octopus(es) to come through?
4) Why do the doppleganger prisoners attack when they are released? They know the next room is a death trap. I had them get weapons and armor from the PCs, and then attack when they trying to cross through the Invisible Stalkers. Much more effective. Too much so, as it turns out!
5) Holy crap are invisible stalkers dangerous! They can fly down, attack, and then retreat without triggering attacks of opportunity. Meanwhile PCs are falling into the water/swords and struggling in general. This room is a death trap!
6) The doppleganger prisoners take some explanation. Presumably there's an elaborate ruse when the guards change so that the elf noble doesn't see them enter and leave as guards?
7) Why is there a prison *and* a Hall of Deception with more prisoners? I'm starting to think that the ecology and logistics of this lair were not thought out, despite having a lavatory.
More questions after prepping for tomorrow:
8) D16 conversion notes don't mention an option to lower the wall with a disable device check. Intentional?
9) Telakin has a Wand of Cure Wounds. How does it work? Only usable by people who can cast Cure Wounds, 7 charges maximum, re-charge d6+1 charges? Anyone can use it? Only 3 charges max?
10) Telakin as a "Frost Great Axe". I think it just does 1d6 extra cold damage? It's not a Frostbrand?
11) As a 12th level caster with 18 INT, I think spell attacks are at +8, not +7? And the DC for spells is 16 not 15?
12) You mention protection from one type of energy attack, but don't mention casting it ahead of time anywhere.
13) D19 has two drow coming out the secret door. Presumably they've already levitated across the water? I thought this was an alternate entrance for the doppelgangers, but that doesn't work - they can't get to the secret door without using the barrel, which would then float aimlessly! And that's even assuming the water is in the room and not drained.