Arcbound Overseer is a rare Artifact Creature — Golem card from The List (PLST), collector number DST-99. Current market price: $4.10, TCGplayer market prices via Scryfall.
At the beginning of your upkeep, put a +1/+1 counter on each creature you control with modular. Modular 6 (This creature enters with six +1/+1 counters on it. When it dies, you may put its +1/+1 counters on target artifact creature.)