Arcbound Slith is a uncommon Artifact Creature — Slith card from Darksteel (DST), collector number 102. Current market price: $0.37 (foil $5.46), TCGplayer market prices via Scryfall.
Whenever this creature deals combat damage to a player, put a +1/+1 counter on it. Modular 1 (This creature enters with a +1/+1 counter on it. When it dies, you may put its +1/+1 counters on target artifact creature.)