Is Stallion of Ashmouth legal in Standard, Modern, and Commander?

Stallion of Ashmouth is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Pauper.

Stallion of Ashmouth

Q: What type of card is Stallion of Ashmouth?

Stallion of Ashmouth is a Creature — Nightmare Horse. Its oracle text reads: "Delirium — {1}{B}: This creature gets +1/+1 until end of turn. Activate only if there are four or more card types among cards in your graveyard. *Echoing hoofbeats can no longer be assumed to be help from the Gavony Riders.* Power/Toughness: 3/3"