Orzhov Terminator

Extort (Whenever you cast a spell, you may
pay {w/b}. If you do, each opponent loses 1 life and
you gain that much life.)
At the end of each turn, if you extorted that
turn, you may tap Orzhov Terminator. If
you do, destroy target creature with power
less or equal to the total life you gained
while extorting in that turn.