Gauntlet of Power is a rare Artifact card from Time Spiral (TSP), collector number 255. Current market price: $3.81 (foil $6.45), 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.