Embereth Skyblazer is a rare Creature — Human Knight card from Throne of Eldraine (ELD), collector number 321. Current market price: $0.34, TCGplayer market prices via Scryfall.
During your turn, this creature has flying. Whenever this creature attacks, you may pay {2}{R}. If you do, creatures you control get +X/+0 until end of turn, where X is the number of opponents you have.