Vampire Hunter D

Ward—Pay 3 life.
Whenever you gain life, Vampire Hunter D
Explores. Then destroy all other
creatures if its power is exactly 20. (To Have
this creature explore, reveal the top card of your
library. Put that card into your hand if it's a
land. Otherwise, put a +1/+1 counter on this
creature, then put that card back or put it into
your graveyard.)