the fusion potara from goku and vegeta he debuted in the buu saga wen goku and vegeta almost got killed by super buu how already absorbed gotenks piccolo and gohan so they fuse to stop him and free his from the interior of majin buu his return was in dragon ball super agains merged zamasu in manga and anime at this point he know that potara fusion is not permanent in mortals thats why goku and vegeta difuse in bout ocations