Flayer of the Hatebound.
So, this guy turns “Undying” into an offensive ability. “Yeah sure kill my creatures, it will only hurt you in the end anyway”.
I can see a lot of decks forming around this guy, only I’m unsure what secondary colour you’d go for… Green? Black? Blue to combine with flashback?
6 mana is steep, but Flayer of the Hatebound is pretty sweat. You get a 4/2, then a 5/3 that hits for a Lava Axe. It’s awesome in multiples, or with any other undying creature.