Post game spoilers

what pokemon are affected by the crystlpieces? I know arceus giratina and Regigigas are but is there another?

Giratina is? What does it do? Ive had giratina hold it before and didnt notice anything, is it just stat improvement?

It should transform it back into the from you caught in with the different sprite and omnitype for an ability like a primal reversion of groudon or kyogre