I'd go with the Mors Gravis demon the least likely. Against gnomes and svirfs, its physical attack is nice, but against those, the mental attacks of the demon are just not worth it. I'd perfer to see the demon be given a different set of special attacks, and change one of the other demons to more mental. Maybe switch the Mors Gravis demon to a more physical role with bashs and such (It is a lumbering demon) and switch the Morosa demon in a more mage based class using those powers from it. On a different note, I'd rather see the Harmentia demon switched to a warrior specs demon, that comes with low level weapons, but if it slays foes with better weapons, it will pick them up and wield those instead. So you can custom its attack and weapons to the needs. Change it too so when its killed the weapons vanish instead of being in the corpse.