Cheapest priced copy (Throne of Eldraine): $0.49 at Card Kingdom, near mint, their price list as of .
Embereth Skyblazer 
Creature — Human Knight · 4/3 · Rare · Throne of Eldraine · #321
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.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Throne of Eldraine | 321 | Rare | $0.49 | — |
3 rulings from Wizards of the Coast
- 4 October 2019The value of X is determined only as Embereth Skyblazer's triggered ability resolves. It doesn't change later in the turn if opponents leave the game.
- 4 October 2019While resolving Embereth Skyblazer's triggered ability, you can't pay {2}{R} multiple times to increase the bonus.
- 4 October 2019In a multiplayer game, opponents who have left the game before the ability resolves aren't counted by Embereth Skyblazer's triggered ability.