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

Maelstrom Muse is legal in: Modern, Pioneer, Legacy, Vintage, Commander.

What type of card is Maelstrom Muse?

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

Maelstrom Muse

Creature — Djinn Wizard

Flying

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