Miriam, Herd Whisperer is a uncommon Legendary Creature — Human Druid card from Outlaws of Thunder Junction (OTJ), collector number 221. Current market price: $0.25 (foil $0.21), TCGplayer market prices via Scryfall.
During your turn, Mounts and Vehicles you control have hexproof. Whenever a Mount or Vehicle you control attacks, put a +1/+1 counter on it.