Gauntlet of Power is a rare Artifact card from The List (PLST), collector number TSP-255. Current market price: $5.04, TCGplayer market prices via Scryfall.
As this artifact enters, choose a color. Creatures of the chosen color get +1/+1. Whenever a basic land is tapped for mana of the chosen color, its controller adds an additional one mana of that color.