Knighted Myr is a common Artifact Creature — Myr Knight card from Modern Horizons 2 (MH2), collector number 17. Current market price: $0.23 (foil $0.30), TCGplayer market prices via Scryfall.
{2}{W}: Adapt 1. (If this creature has no +1/+1 counters on it, put a +1/+1 counter on it.) Whenever one or more +1/+1 counters are put on this creature, it gains double strike until end of turn.