Relek, Endless Void

This spell can't be countered.
Flying, Hexproof, Crippling 2 (at the beginning
of every opponent's turn, all their creatures get a
-2/-2 counter)
When this card enters the battlefield, destroy all
creatures you control. For each creature
destroyed this way, force an opponent to sacrifice
a creature they control.
If an opponent does anything to affect this card
other then blocking it, they lose the game.