Brain Tap

You tap directly into the mind of a foe, draining its intelligence.  Make a melee spell attack against a creature within your reach.  On a hit, the target takes 3d6 psychic damage and must make an Intelligence saving throw.

On a failed save, until the beginning of your next turn it cannot speak and doesn't understand spoken or written language.  Until the spell ends, you can repeat the attack as an action, though the target does not repeat the save.

At Higher Levels.  When you cast this spell using a spell slot of 4th level or higher, the psychic damage increases by 1d6 for each slot level above 3rd.