Seishi, Oni King

Commander ninjustu {1}{p/u}{p/b}{p/r}
Eminence -- Whenever a Ninja you control deals
combat damage to a player, if Seishi, Oni King is
in the command zone or on the battlefield, you
may pay {p/u}{p/b}{p/r}. If you do, destroy target
creature that player controls. You gain life equal
to that creature's toughness
Ninja creatures you control have Lifelink.