I think his spell is fine (except I swear I have only seen two summons for the longest time when it does kill something). It starts off slower than drac and suna steals from 2 targets, but it does scale better with the magic steal. It could either apply curse and death mark to the target as well or drain mana just like Morthani’s Will.
Since The Gray King has the 4+ match buffs, Xathenos should be at the start of every turn. For this other traits, personally I’d like impervious with either arcane or mana shield but I’d also accept necromancy as it would be thematically fitting.
Here’s the link to the most recent thread by @TheIdleOne