Mystic Forge is a rare Artifact card from Modern Horizons 3 Commander (M3C), collector number 302. Current market price: $5.33, TCGplayer market prices via Scryfall.
You may look at the top card of your library any time. You may cast artifact spells and colorless spells from the top of your library. {T}, Pay 1 life: Exile the top card of your library.