+1: Until your next turn, instant and sorcery spells you cast cost 1 less to cast
If you are lucky enough to open a textured foil, you just pulled one of the most valuable cards, and even the base version has a decent price if you don't get the fancy art treatment in your pack
Essentially, the target must discard one card per black mana used, making it a super powerful option capable of winning games for players
Plus the helm is better in some cases
The most rare, and most valuable one is the three-color Neon Ink variant, which has a less than 1% chance of opening a Special Guest card at all, and an even smaller chance of opening this three-colored iteration.
Offering buffs, protection, life gain, and reanimation , Sword of Light and Shadow can be incredibly useful in a great many decks