Wildwood Mentor is a rare Creature — Treefolk card from Wilds of Eldraine (WOE), collector number 374. Current market price: $0.99, TCGplayer market prices via Scryfall.
Whenever a token you control enters, put a +1/+1 counter on this creature. Whenever this creature attacks, another target attacking creature gets +X/+X until end of turn, where X is this creature's power.