This is a really polished entry! The art style stands out, especially the animations (the Mad Prisoner cartwheeling around was a great touch). The music is also good but very loud and repetitive, so I had to turn the volume way down and ended up muting it altogether (though I loved how the different bosses had different themes). I also enjoyed the mood and the little snippets of conversations as you follow your cellmates around.
My biggest gripe is that I found some symbols confusing. It took a room or two for me to even recognize the spikes as such. Also, it seems you can't avoid taking damage in some instances which led to me being stuck forever in the first few rooms because the first time I tried to bump into the star-shaped thingy, it killed me outright. Assuming it was an enemy I couldn't dispatch yet, I let it alone when the solution was to purposefully get hurt. This was made worse by the chest in the room right before it because I thought I was supposed to open it but couldn't and didn't know why. It's only later that I managed to open some, though I'm still not 100% certain it was thanks to the keys I collected. It's really missing feedback on that front.
I didn't get too far because that's not really my kind of game (it's not an action-adventure game, so I don't really consider it a metroidvania, but I know the jam's pretty flexible on that front), but it was definitely interesting if a bit opaque and frustrating. With improved feedback it could lead to something really special. Good job! ;)