Collective Inferno is a rare Enchantment card from Lorwyn Eclipsed (ECL), collector number 363. Current market price: $2.03 (foil $2.01), 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.) As this enchantment enters, choose a creature type. Double all damage that sources you control of the chosen type would deal.