Anivia, the Cryophoenix

Flying
When Anivia, the Cryophoenix enters the battlefield an opponent chooses Attack or Block.
Creatures can't perform the chosen action.
A player may pay {w/u} for a creature to ignore this ability until end of turn.
I am the fury of the blizzard, the bite of the wind, and
the cold of the ice. I am the Freljord.