Veseril, Thought Reaver

Flying
Whenever a player casts or copies a spell, target
player mills four cards.
Whenever an opponent mills or discards one or
more cards you may pay {u/b} and 1 life. If you do,
choose and exile a card from among them and put
a Reave counter on it.
Pay 2 life : You may cast target spell from exile
with a Reave counter on it this turn and you may
spend mana as though it were mana of any type
to cast that spell.