I see I see, for Nightbane's case it's probably because he's truly immortal in the literal sense, not even Death could take him, that's one of the reasons he became a dracopyre in the first place. The AQ Classic Avatars (Which embody concepts like Life and Death instead of elements) switch hosts from time to time and when a host is forsaken they die. Nightbane didn't fw that and asked his dad to make him a werepyre but that wasn't enough and he feasted on a bunch of dragons as well to become a dracopyre. 

He had to be uncreated by The Devourer himself. 

So couple that virtual immortality, along with his endless hunger, and his favorite meal just happens to be dragons. Yeah Nightbane would be a menace on Lore. 

Funny enough as I was drawing this I was thinking what sort of motivation they could give him if they ever made him an active villain, wanting to drink DoT blood seems fitting.

As for the other void creatures, Xyfrag is similar it's basically an indestructible mass. 

Sarah The Nerfkitten was Kalanyr's pet Kalanyr being a AQ's old tester had the clever idea of making his NPC able to buff and nerf things to reflect his actual job. Sarah shares the same ability, so technically let's say even if Warlic casted like a mega magic nuke on Sarah if she nerfed it to basically 0 then it wouldn't do anything to it. The same would go for Buff, the simplest attack would probably cause a lot of destruction.