Sarkhan's Unsealing is a rare Enchantment card from Jumpstart (JMP), collector number 361. Current market price: $1.03, TCGplayer market prices via Scryfall.
Whenever you cast a creature spell with power 4, 5, or 6, this enchantment deals 4 damage to any target. Whenever you cast a creature spell with power 7 or greater, this enchantment deals 4 damage to each opponent and each creature and planeswalker they control.