Dionus, Elvish Archdruid is a uncommon Legendary Creature — Elf Druid card from Foundations Jumpstart (J25), collector number 52. Current market price: $16.08, TCGplayer market prices via Scryfall.
Elves you control have "Whenever this creature becomes tapped during your turn, untap it and put a +1/+1 counter on it. This ability triggers only once each turn."