Coin of Mastery is a rare Artifact card from Teenage Mutant Ninja Turtles Eternal (TMC), collector number 38. Current market price: $1.51 (foil $2.00), TCGplayer market prices via Scryfall.
Each creature you control enters with an additional +1/+1 counter on it for each mana from an artifact source spent to cast it. {T}: Create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")