Autonomous Assembler is a rare Artifact Creature — Assembly-Worker card from The Brothers' War (BRO), collector number 34. Current market price: $0.19 (foil $0.23), TCGplayer market prices via Scryfall.
Prototype {1}{W} — 2/2 (You may cast this spell with different mana cost, color, and size. It keeps its abilities and types.) Vigilance {1}, {T}: Put a +1/+1 counter on target Assembly-Worker you control.