Is Embereth Skyblazer legal in Standard, Modern, and Commander?

Embereth Skyblazer is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Historic.

Embereth Skyblazer

Q: What type of card is Embereth Skyblazer?

Embereth Skyblazer is a Creature — Human Knight. Its oracle text reads: "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."

Creature — Human Knight

During your turn, this creature has flying.

Whenever this creature attacks, you may pay . If you do, creatures you control get +X/+0 until end of turn, where X is the number of opponents you have.