Wubryx, the necrospeller

Whenever an opponent mills one or more cards,
you get a necrospell counter.
Pay 3 necrospell counters: Choose one:
-Each opponent loses 3 life.
-Draw a card.
-You may exile target card from a graveyard, if
you do, you may play it as long as is exiled.
You may spend mana of any color to cast it or
activate it's habilities.