These are two different beings. One is an “angel”, a renamed Mesopotamian god, the other, ime is nothing more than a parasite from Dante Abiel’s book on Necromancy. My gnosis is that it was a lesser entity (actually a dead human trying to be immortal, like the loa) worshiped by what was basically death cult and almost killed him, now he’s run back to xtianity to save himself from it - and if jehova of all things is more powerful than it, that tells you everything you need to know about it’s ability, or the lack thereof.
My advice is stay away from it, it will eat you alive, reflect your own power back at you and pretend it gave it to you. It would have got me but I already had Belial inside me and he dealt with it.
So I’ve met both and it makes no sense to me to conflate them on any level. So, why did you do that? What happened to make you think a god of death has a “dark side” that is darker than being a god of death? And what did that parasite say to trick you into working with it?
Just out of curiosity.