Nadina, Purple Dawn

{u/b}{u/b}{u/b}, Exile 20 cards from the top of your
library during your turn: Put this onto the
battlefield from anywhere, then draw 4.
Flash, evoke {u/b} or {2} or {4}, flying, menace
When cast — For each mana spent to cast
this, put a -1/-1 counter on target
permanent.