I know, I said two days, too bad = P
So here is my Mega Metagross, Attack and Defense form ~
When mega-evolving, he obtains "Stance Change", and if Metagross has a capacity like "Agility" for example in his moveset, it's replaced by "King's Shield" during the time of the transformation ~
His two back arms fuses and become his main magnetic source.
P.S. : I don't want to see comments about "is it fit with Metagross stats?" or simply "it's not a good thing for Metagross" because I wanted a two form Metagross which weren't something like X and Y form, and there was a good capacity in 6G to exploit. So it's mainly design than statistics here.