Karn, Legacy Reforged is a mythic Legendary Artifact Creature — Golem card from Mystery Booster 2 (MB2), collector number 255. Current market price: — (foil $48.01), TCGplayer market prices via Scryfall.
Karn's power and toughness are each equal to the greatest mana value among artifacts you control. At the beginning of your upkeep, add {C} for each artifact you control. This mana can't be spent to cast nonartifact spells. Until end of turn, you don't lose this mana as steps and phases end.