Green Sun's Zenith is a rare Sorcery card from Mirrodin Besieged (MBS), collector number 81. Current market price: $32.13 (foil $78.01), TCGplayer market prices via Scryfall.
Search your library for a green creature card with mana value X or less, put it onto the battlefield, then shuffle. Shuffle Green Sun's Zenith into its owner's library.