Timesifter is a rare Artifact card from Mirrodin (MRD), collector number 262. Current market price: $4.00 (foil $17.37), TCGplayer market prices via Scryfall.
At the beginning of each upkeep, each player exiles the top card of their library. The player who exiled the card with the greatest mana value takes an extra turn after this one. If two or more players' cards are tied for greatest, the tied players repeat this process until the tie is broken.