Is Hell Mongrel legal in Standard, Modern, and Commander?

Hell Mongrel is legal in: Modern, Legacy, Vintage, Commander, Pauper, Historic.

What type of card is Hell Mongrel?

Hell Mongrel is a Creature — Nightmare Dog. Its oracle text reads: "Discard a card: This creature gets +1/+1 until end of turn. Madness {2}{B} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)"