Probably not a bug but it was something that I spotted and thought it was odd. I tried to figure out the original Hexen behaviour but didn't find anything meaningful.
The Demon2FX1 actor (the green ball of gas belched by the Demon2 brown chaos serpent) has a damage type of "Fire". It just struck me as odd given that it looks like a green ball of [poison] gas versus the much more obviously fire-like appearance of the green Demon1's attack.
The obituary for Demon2 even says "%o was poisoned by a Serpent." versus "%o was scalded by a Serpent." for Demon1.
Obviously, if it matches the Hexen behaviour then it should stay as it is.