Crowd's Favor is a common Instant card from The List (PLST), collector number M15-138. Current market price: $0.24, TCGplayer market prices via Scryfall.
Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.) Target creature gets +1/+0 and gains first strike until end of turn. (It deals combat damage before creatures without first strike.)