I think that Regigigas should get a mega. It would delete that stupid ability, boost all of its stats but its speed, and look something like this.
(link)
http://th02.deviantart.net/fs71/PRE/i/2014/245/e/2/mega_regigigas_by_the_e_guess_corner-d7xpqmq.png
(link)
http://th02.deviantart.net/fs71/PRE/i/2014/245/e/2/mega_regigigas_by_the_e_guess_corner-d7xpqmq.png