Nekusar, Eldritch Warden

Undying
Whenever you cast an instant or sorcery spell,
create a 2/2 black Zombie creature token with
menace and afflict 1.
Whenever an opponent casts a creature card, you
may pay {u}{b}{r}. If you do, cast target instant or sorcery card from a graveyard without paying its
mana cost. If it would be put into a graveyard this
turn, exile it instead.