Stromkirk Bloodthief is a uncommon Creature — Vampire Rogue card from Innistrad: Double Feature (DBL), collector number 123. Current market price: $0.33 (foil $0.77), TCGplayer market prices via Scryfall.
At the beginning of your end step, if an opponent lost life this turn, put a +1/+1 counter on target Vampire you control.