Tenacious Pup is a uncommon Creature — Wolf card from Mystery Booster 2 (MB2), collector number 262. Current market price: — (foil $36.56), TCGplayer market prices via Scryfall.
When Tenacious Pup enters the battlefield, you gain 1 life. You get a one-time boon with "When you cast a creature spell, that creature enters the battlefield with an additional +1/+1 counter, trample counter, and vigilance counter on it."