Manacineration

(You may cast a legendary spell only if you control a legendary creature or Planeswalker.)

Choose X mana colors. Destroy all
permanents of the chosen color that you do
not control. For every permanent destroyed
this way, all opponents mill and then discard
that many cards, split evenly between them.
If at least 3 Planeswalkers were destroyed
this way, you win the game.