Trostani, Selesnya's Voice is a mythic Legendary Creature — Dryad card from GRN Guild Kit (GK1), collector number 102. Current market price: — (foil $2.92), TCGplayer market prices via Scryfall.
Whenever another creature you control enters, you gain life equal to that creature's toughness. {1}{G}{W}, {T}: Populate. (Create a token that's a copy of a creature token you control.)