Battlefield Promotion is a common Instant card from War of the Spark (WAR), collector number 5. Current market price: $0.15 (foil $0.45), TCGplayer market prices via Scryfall.
Put a +1/+1 counter on target creature. That creature gains first strike until end of turn. You gain 2 life. (A creature with first strike deals combat damage before creatures without first strike.)