Chaos Dragon Levianeer

Flying
You may exile White or Black cards from your graveyard, this creature costs X less to cast where X
is the total mana value of the exiled cards.
This card gains the following effects depending on
the color of the creatures exiled to cast this spell:
•White - Put 1 creature from your graveyard onto your battlefield tapped, it does not untap during your next untap step.
•Black - This creature gains double-strike.