Your eyes gloss over as you speak of ennui, failure, and loss. A targeted creature, that can hear, must make an Intelligence save. On failure, the creature is reduced to accessing only the simplest of thoughts, using only basic attacks (or multi-attacks if they have them) and cantrips for their next turn. Creatures that have them can still use legendary and lair actions. Every following turn, if concentration is still maintained by the spellcaster, the creature can attempt another Intelligence save. On success, the spell ends, and the creature can attack as they wish.