Faith Lehane, Rogue Slayer

Ward—Pay 3 life.

Whenever you gain life, Faith Lehane 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 the card back or put it
into your graveyard.)