Dragonfire Blade is a rare Artifact — Equipment card from Tarkir: Dragonstorm Promos (PTDM), collector number 240p. Current market price: $1.50 (foil $1.23), TCGplayer market prices via Scryfall.
Equipped creature gets +2/+2 and has hexproof from monocolored. Equip {4}. This ability costs {1} less to activate for each color of the creature it targets.