Maddening Hex is a rare Enchantment — Aura Curse card from Secret Lair Drop (SLD), collector number 2675. Current market price: $3.70 (foil $4.09), TCGplayer market prices via Scryfall.
Enchant player Whenever enchanted player casts a noncreature spell, roll a d6. This Aura deals damage to that player equal to the result. Then attach this Aura to another one of your opponents chosen at random.