Is Marshmist Titan legal in Standard, Modern, and Commander?

Marshmist Titan is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Pauper.

What type of card is Marshmist Titan?

Marshmist Titan is a Creature — Giant. Its oracle text reads: "This spell costs {X} less to cast, where X is your devotion to black. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)"

Marshmist Titan

Creature — Giant

This spell costs less to cast, where X is your devotion to black. (Each in the mana costs of permanents you control counts toward your devotion to black.)