Altar of the Goyf is a uncommon Kindred Artifact — Lhurgoyf card from Modern Horizons 2 (MH2), collector number 220. Current market price: $0.27 (foil $0.35), TCGplayer market prices via Scryfall.
Whenever a creature you control attacks alone, it gets +X/+X until end of turn, where X is the number of card types among cards in all graveyards. Lhurgoyf creatures you control have trample.