Descendant of Masumaro is a uncommon Creature — Human Monk card from Saviors of Kamigawa (SOK), collector number 126. Current market price: $0.10 (foil $0.39), TCGplayer market prices via Scryfall.
At the beginning of your upkeep, put a +1/+1 counter on this creature for each card in your hand, then remove a +1/+1 counter from this creature for each card in target opponent's hand.