Marketback Walker is a rare Artifact Creature — Construct card from Aetherdrift Promos (PDFT), collector number 235p. Current market price: $0.38 (foil $0.74), TCGplayer market prices via Scryfall.
This creature enters with X +1/+1 counters on it. {4}: Put a +1/+1 counter on this creature. When this creature dies, draw a card for each +1/+1 counter on it.