So here's the setup: a group of characters are trapped behind a metal door in a subway. There is a dead demon in the room that they killed with firearms. I'm trying to come up with the physiology of said demon. I've decided that part of its physical makeup will be sulfur (brimstone = sulfur). I'm thinking they could use the demon's physiology to escape the room. It is your traditional fireball throwing red horned demon. Perhaps they have a gland that secretes some sulfur-based contact explosive in order to create the fireballs, or something that allows them to spit sulfuric acid. Perhaps they can manifest a thermite-like compound that could melt through metal. I don't know enough about chemistry to really know what is possible; I have no idea realistically how long it would take for sulfuric acid to dissolve enough of a door or metal bars in order for one to make an exit. So, what do you think would be most feasible, in a hard sci-fi sense? Obviously demons would have a magical element to them - perhaps they could synthesize volatile chemicals at a faster rate than physics would allow, and perhaps their body parts can go on living after their vital parts are destroyed - but you know, as realistic as reasonable.