Shizuko, Caller of Autumn is a rare Legendary Creature — Snake Shaman card from Betrayers of Kamigawa (BOK), collector number 144. Current market price: $4.06 (foil $13.33), TCGplayer market prices via Scryfall.
At the beginning of each player's upkeep, that player adds {G}{G}{G}. Until end of turn, they don't lose this mana as steps and phases end.