Maddening Hex is a rare Enchantment — Aura Curse card from Forgotten Realms Commander (AFC), collector number 301. Current market price: $3.86, 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.