So far in v0.31.03 we're familiar with dwarves, elves and whatnot bleeding to death when hit by dragonfire. The skin gets destroyed but before the rest of the creature is burnt up the game registers them dead due to blood loss since the skin no longer holds it in.
I wondered what would happen if there was more than one dragon trying to burn the guinea pigs at a time. So why not 30? My platoon of dragons found they actually could cause "Dwarf X melted" deaths (provided they didn't bite and rip them apart in melee). The basic rule is that you need to raise the temperature much faster than a single dragon can - multiple dragon breaths need to hit near simultaneously. To make it easier, pile up all the guinea pigs in 1 tile, and pile up some more guinea pigs on the same tile that are on the same team as the dragon squadron. Dragon fire toasts friend and foe alike, so you're guaranteed some guinea pigs only getting hit by fire and not by lethal dragon teeth.
Also while experimenting, I tried out various other species for burning. Since "bled to death" happens when enough blood drains out from the destroyed skin, turns out bigger specimens melt more often - their insides reach the melting point before all their blood is lost. Polar bears and whales are my staple for when I want to see some melting action, and one time I was lucky enough to see an exploding polar bear due to boiling blood. Sadly, that's a very rare event compared to melting. Hmm, maybe if mutants are modded in with extra low boiling points... Back on subject, one surprise was that harpies also tended to melt rather than bleed. Are they really that much bigger than regular human women or is it their wings that give them extra blood capacity?
Oh and one other thing: Fire Imps suck at burning their targets at range. Sure yes, they have a body temperature hot enough that any blood splatters boil away soon after a fight is over, so they could (in theory) burn their targets down by wrestling them. But they have a tendency to bite. They toss 1 fireball then run up to take bites out of their target. That first fireball volley, even when there's 40 imps, has difficulty killing even a lone elf. Indeed, that one no-skill elf went on to kill a few imps despite being horrendously outnumbered before inevitably going down. Imps are still to be feared for causing collateral damage, but in pure combat they're not worthy enemies.