Spirit of Decay

Extort (Whenever you cast a spell, you may pay {b}. If you do, each opponent loses 1 life and you gain
that much life.)
Whenever you tap a Swamp for mana, add an additional {b}. (In addition to the mana the land
produces.)

"We are merely the vectors by which his virulent beneficence may be spread to the undeserving masses."