Mosquito Guard is a common Creature — Kithkin Soldier card from Duel Decks: Elspeth vs. Tezzeret (DDF), collector number 6. Current market price: $0.21, TCGplayer market prices via Scryfall.
First strike Reinforce 1—{1}{W} ({1}{W}, Discard this card: Put a +1/+1 counter on target creature.)