Keen Duelist is a rare Creature — Human Wizard card from Commander 2021 (C21), collector number 369. Current market price: $2.49, TCGplayer market prices via Scryfall.
At the beginning of your upkeep, you and target opponent each reveal the top card of your library. You each lose life equal to the mana value of the card revealed by the other player. You each put the card you revealed into your hand.