Don't know if its been mentioned before, but the name of the plague turtle sounds a lot like the german "Krankheit", meaning disease/sickness. Wouldn't be the first time a random german word gets used.
Couldn't he have just released Eligos from her contract once he got hold of the ring and all his problems would have been solved?
Him going after the other demons and being angry about the ring loosing value makes it seem like the flashback was an afterthought to make him more sympathetic (which...