Traverse the Void-Rift

You may pay {x} rather than pay the mana costs
of spells you cast that are both black and white,
where X is that spell's mana value.
At the beginning of your end step, sacrifice a permanent. If you do, search your library for a
card that's both black and white and shares a
card type with the sacrificed permanent, reveal
it, put it into your hand, then shuffle. If you
control another Void permanent, target player sacrifices a creature.