Altar of the Goyf is a uncommon Kindred Artifact — Lhurgoyf card from Modern Horizons 3 Commander (M3C), collector number 282. Current market price: $0.24, 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.