Dark Knight of Ren

Flash, Deathtouch
When you cast Dark Knight of Ren, you may sacrifice a creature. If you do, you add X black
mana to your mana pool and gain life where X is
the sacrificed creature's toughness.
When Dark Knight of Ren dies, you may search
your library and graveyard for Knight of Ren and
put it into your hand. If you searched your
library, shuffle it.