Unspeakable Insight

You fill a creature's mind with insights too terrible to be borne, wreathing it in eldritch energies. One creature you can see or telepathically sense within range must succeed on a Wisdom saving throw or gain 20 temporary hit points.

While a creature has any of these temporary hit points, its Intelligence score increases by 5, to a maximum of 25. At the end of its turn, a creatures loses all of the temporary hit points and takes psychic damages equal to twice the temporary hit points lost.