Sakiko, Mother of Summer is a rare Legendary Creature — Snake Shaman card from Betrayers of Kamigawa (BOK), collector number 141. Current market price: $1.56 (foil $14.99), TCGplayer market prices via Scryfall.
Whenever a creature you control deals combat damage to a player, add that much {G}. Until end of turn, you don't lose this mana as steps and phases end.