Comeuppance is a rare Instant card from Murders at Karlov Manor Commander (MKC), collector number 58. Current market price: $5.16, TCGplayer market prices via Scryfall.
Prevent all damage that would be dealt to you and planeswalkers you control this turn by sources you don't control. If damage from a creature source is prevented this way, Comeuppance deals that much damage to that creature. If damage from a noncreature source is prevented this way, Comeuppance deals that much damage to the source's controller.