Velris, Voidwalker

Whenever an opponent draws one or more cards, exile the top card of their library with a void counter.
You may cast cards from exile with a void counter on it for {2} less, and spend mana as though it were mana of any color to cast them.
{1}{u/b}{u/r}{b/r}, {t}: Target opponent may cast cards they own from exile with a void counter on it until end of turn, but lose 1 life for each card they cast this way.