Grave Strength is a uncommon Sorcery card from Ultimate Masters (UMA), collector number 101. Current market price: $0.25 (foil $0.29), TCGplayer market prices via Scryfall.
Choose target creature. Mill three cards, then put a +1/+1 counter on that creature for each creature card in your graveyard. (To mill three cards, put the top three cards of your library into your graveyard.)