Marwyn, the Nurturer is a rare Legendary Creature — Elf Druid card from Dominaria (DOM), collector number 172. Current market price: $7.36 (foil $9.29), 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.