Assume True Form

You create an aura around yourself that forces all shapeshifted creatures to resort to their normal forms. The spell affects lycanthropes, therianthropes, doppelgangers, mimics, and creatures under the effect of polymorph magic. A shapechanged creature that begins its turn within the aura is forced to resume its natural form unless it makes a successful
Constitution saving throw. If the saving throw fails, it reverts to its normal form immediately, and it can’t alter its form voluntarily again until it leaves the spell’s area of effect.