Is A-Maelstrom Muse legal in Standard, Modern, and Commander?

A-Maelstrom Muse is legal in: Historic.

A-Maelstrom Muse

Q: What type of card is A-Maelstrom Muse?

A-Maelstrom Muse is a Creature — Djinn Wizard. Its oracle text reads: "Flying Whenever Maelstrom Muse attacks, the next instant or sorcery spell you cast this turn costs {X} less to cast, where X is Maelstrom Muse's power as this ability resolves. Power/Toughness: 2/4"

Creature — Djinn Wizard

Flying

Whenever Maelstrom Muse attacks, the next instant or sorcery spell you cast this turn costs less to cast, where X is Maelstrom Muse's power as this ability resolves.