Monoskelion is a uncommon Artifact Creature — Construct card from Modern Horizons 2 (MH2), collector number 229. Current market price: $0.19 (foil $0.33), TCGplayer market prices via Scryfall.
This creature enters with a +1/+1 counter on it. {1}, Remove a +1/+1 counter from this creature: It deals 1 damage to any target.