Trostani, Selesnya's Voice is a mythic Legendary Creature — Dryad card from The List (PLST), collector number GK1-102. Current market price: $1.35, 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.)