First go to the item shop and buy "one who loves justice" and "king yemma's stamp"
P.S. these are purple potaras.
if you fuse them you get a yellow potara named halo.
put these on the evolution Z of goku or vegeta.
and in battle you see a halo above the head of goku or vegeta.
more can use it but they don't get the halo on their heads, but get the efect of halo........ the effect of halo is blast 2's and ultimate blasts wil cost only the half of energy you usely use.