Bringing Aggramar back isn't that hard. He was just cleaved in half by Sargeras, his soul would still be there. Technically, Sargeras can capture that soul (from Shadowland?) and twist him, give him a new body and such. Eonar is the bigger question I think. Her soul should have been sent to Azeroth together with the rest, so what exactly is here? An empty body without soul? A fragment of soul for some reasons left behind? Or Eonar herself somehow managed to regain her body, came to assault Sargeras in revenge and got captured & twisted?
Anyway, there goes that poster (can't remember the name)'s theory of Eonar being Elune.