Myr Prototype is a uncommon Artifact Creature — Myr card from Mirrodin (MRD), collector number 214. Current market price: $0.18 (foil $1.77), TCGplayer market prices via Scryfall.
At the beginning of your upkeep, put a +1/+1 counter on this creature. This creature can't attack or block unless you pay {1} for each +1/+1 counter on it.