Pack's Favor is a common Instant card from Guilds of Ravnica (GRN), collector number 139. Current market price: $0.10 (foil $0.44), 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 +3/+3 until end of turn.