Feeblemind

You blast the mind of a creature within the spell’s range, attempting to shatter its intellect and personality. The target takes 4d6 psychic damage and must make an Intelligence saving throw.

On a failed roll, its Intelligence and Charisma become 1. The creature cannot cast spells, activate magical items, understand languages or communicate intelligibly. It can identify its friends, follow them and even protect them.

At the end of a 30-day period, the creature may take the magic saving throw again. On a successful save, the magic is dispelled. It can also be dispelled by Greater Restoration, Heal or Wish.