Is Impulsivity legal in Standard, Modern, and Commander?

Impulsivity is legal in: Legacy, Vintage, Commander.

What type of card is Impulsivity?

Impulsivity is a Creature — Elemental Incarnation. Its oracle text reads: "When this creature enters, you may cast target instant or sorcery card from a graveyard without paying its mana cost. If that spell would be put into a graveyard, exile it instead. Encore {7}{R}{R} ({7}{R}{R}, Exile this card from your graveyard: For each opponent, create a token copy that attacks that opponent this turn if able. They gain haste. Sacrifice them at the beginning of the next end step. Activate only as a sorcery.)"

Impulsivity

Creature — Elemental Incarnation

When this creature enters, you may cast target instant or sorcery card from a graveyard without paying its mana cost. If that spell would be put into a graveyard, exile it instead.

Encore (, Exile this card from your graveyard: For each opponent, create a token copy that attacks that opponent this turn if able. They gain haste. Sacrifice them at the beginning of the next end step. Activate only as a sorcery.)