Jackknight is a rare Artifact Creature — Cyborg Knight card from Unstable (UST), collector number 11. Current market price: $0.26 (foil $0.77), TCGplayer market prices via Scryfall.
Whenever another artifact you control enters, put a +1/+1 counter on this creature. If that artifact is a Contraption, this creature gains lifelink until end of turn.