Soul Burn is a common Sorcery card from Deckmasters (DKM), collector number 9. Current market price: $0.25, TCGplayer market prices via Scryfall.
Spend only black and/or red mana on X. Soul Burn deals X damage to any target. You gain life equal to the damage dealt, but not more than the amount of {B} spent on X, the player's life total before the damage was dealt, the planeswalker's loyalty before the damage was dealt, or the creature's toughness.