Stallion of Ashmouth is a common Creature — Nightmare Horse card from Shadows over Innistrad (SOI), collector number 136. Current market price: $0.06 (foil $0.15), TCGplayer market prices via Scryfall.
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.