I'm actually really excited about a cave-themed mafia. I've just been thinking about all the ways I would do it if it were me. I'm sure Amy has something spectacular in mind already, but this is what came to mind:
A) For flavour purposes, it's easiest to make all characters humans (because wouldn't everyone notice you were actually a bat, barring vampirism?). One possible motivation is that one group is seeking a mysterious artifact hidden deep within the cave, but the infiltrating group knows what the artifact is and doesn't want it to be uncovered.
B) The death mechanic is best explained by a weather event flooding the cave entrance and wedging a boulder in place a la Sanctum. With only a meager amount of food on hand, each day the team must decide to abandon someone so that they can stretch their food further (either by blocking them up in a room and dropping rocks in front of it, or swimming to the other end of a long sump and taking their oxygen tanks with them, or climbing up somewhere and pulling the rope up after them).
C) Tied in with the above flavour would be a role on each team of a "cave rescue", someone who can bring back a previous lynchee exactly once. The scum team would have it as a night action, while the town one would announce who'd they are rescuing publicly in the thread. (The scum one could also announce before the scum partner they rescued starts talking again, if they want to muddy the waters.)
D) The town team could also have a paranoid claustrophobe who brought a gallon bucket of batteries because they refuse to sleep with the lights off, and can hardly sleep at all. As such, they see things that happen in the night. (A tracker who, if they do not follow a particular person, just receives a message about someone random who was "moving around at night".)
E) One team could have a "survivalist" who is really strong and good at making meals of bats and crickets and blind fish, and so can continue talking for a day or two if they are lynched.
F) Someone should have a video camera, like in Descent that they can aim at a particular player overnight (e.g. a Watcher), but only a limited number of times (batteries and all that jazz).
G) Mafia kills should be in the form of sabotaged equipment. Punctured air hose, knifed harness, etc. and they don't actually die until halfway through the next day (e.g. we went to climb up, but you fell down and died!). Which gives them time to share any information they uncovered IF they can guess that they were targeted.
H) Who's on Team Hodag? That is all.
Of course, with all these ideas, I have no idea how I would balance it, but I can really see myself getting into the flavour of it. I'd kinda want to do the whole thing in character. Looking forward to whatever Amy comes up with!