Okay first off, this is a great idea and I love it, but as of now there are a few things to look at. (Side note, I managed to get through most of the first floor, skeleton keeps kicking my ass, seriously are you supposed to go back and kill them later? Because as of now I'm just grinding rats and bats to try and kill them, and I've ran into multiple setups where the stairs were behind the skeleton, so I either had to kill them or make a mad dash and hope a rat or bat never cuts me off.)
The posession, while it works well and I like the concept (posessing creatures, maxing them out, then basically using them as free heals), as it keeps the idea that you are a little imp dude and not whatever thing you're posessing at the time. There's a reason to deposess, and a pretty big one. Very good! I'm assuming later monsters will be bigger and more useful to "hang out in", so I'm leaving out that there's unfortunately not really a reason to stay inside of anything, because presumably later on there will be. The difficulty also seems pretty steep even for a roguelike, it seems like I spend most of the first floor or two at least running away from skeletons and trying to kill as many rats and bats as possible which really, at the end of the day just comes down to grinding.
Minor niggling stuff, music is okay for a little bit but the fact that there's a single track makes it grind on the ears a bit. Might look into making a few different tunes. There needs to be a map, period. Even if you're not supposed to grind out full floors it's good to have one to know how to get to where you need to be. I'm presuming it's on the way, because it seems kinda odd that it's missing entirely.
Finally, please add a way to know if you've hit something or missed it without the audio cues, again as I went along I found out it was fairly minor but it'd be good to know if an envenom or life leech for instance, landed on an enemy. Also of note, maybe a way to tell if enemies are poisoned or whatever.
I like the concept and I'm looking forward to see where this goes so keep at it!
EDIT: Oh, I missed the F menu completely. That's very handy! And might solve some of my complaints. (doubledit: it does, I've scratched out the parts I no longer really have an issue with currently) But brings up another point, why isn't that in the game start paragraph? Honestly just saying "check out the readme to learn how to play" would probably be better, but maybe some form of in game tutorial was required for the game jam this was a part of? Anyway. Back to fiddling.