Here is a team fairly focussed on a CM Stored Power Mega Latias sweep. Mega Latias' kit is designed to be an extremely effective CM Sweeper once its checks are removed, namely dark types. It has the bulk, recovery and way of avoiding status necessary for making set up very easy once those that can break Mega Latias are removed. Ferrothorn was necessary to use and acts as an efficient sponge to most attacks directed at Latias, particularly bug, dragon and fairy attacks. Ferrothorn is also my best answer to Mega Gyarados and sets spikes, drastically helping Gliscor, Emboar and Jirachi clean if need be. Cobalion was the next choice as it is a terrific dark type check to threats such as Bisharp, Tyranitar, Hydreigon, Crawdaunt, Mega Sharpedo, and Mega Absol. SD Specially defensive Gliscor was a necessary addition for a second win con and consistant answer to Gengar. Also beats Mega Sableye. Choice Scarf Emboar is likely the most underrated yet valuable member to this team. It can reliably switch into and beats Bisharp, Tyranitar, Mega Sableye, Mega Houndoom, Mega Absol (without Superpower), and revenge kills all those mentioned as well as Hydreigon, Pangoro, and Mega Gyarados (assuming it hasn't boosted its speed). As well as many other non dark types obviously but these are important to the team's main function. Note that Emboar has just enough speed EVs to out speed Scarf or +1 DD T-Tar. Scarf Rachi gets a bit of Volt-Turn going with Cobalion and abuses Iron Head / Zen Headbutt along side Cobalion's Thunder Wave to hax the enemy to death. Jirachi is also here to patch up the team's nasty weakness to Mega Gardevoir. Healing Wish is invaluable as it can extend Emboar's timer, or give Mega Latias or Gliscor a second chance to sweep if you misplay with them early on.