Marwyn, the Nurturer is a rare Legendary Creature — Elf Druid card from Dominaria Promos (PDOM), collector number 172p. Current market price: $5.85 (foil $10.28), TCGplayer market prices via Scryfall.
Whenever another Elf you control enters, put a +1/+1 counter on Marwyn. {T}: Add an amount of {G} equal to Marwyn's power.