I decided on
Glare Serperior +
Band Tyranitar right off the bat, since Serperior can make up for some of Tyranitar's poor speed issues, which hinder it in trapping or KOing Serperior's checks (i.e. Surf Specs Latios, Superpower Tornadus-T, WoW Talonflame).
Chople Magnezone removes Steel-types that stop Tyranitar and Serperior from spamming Grass and Rock moves, since neither really like wasting precious PP like that. Chople lets it check stuff like fast Superpower Mega Scizor/Tornadus-T and Focus Blast Thundurus, and emergency check to a few Fighting-types; Thunder Wave is helpful because with two Substitute users and a DDer I'd often rather have something paralyzed than KOed, and it makes a great Mega Lopunny lure.
Defensive Landorus-T is kind of a no-brainer here, it sets rocks and checks most physical attackers, especially Fighting- and Ground-type ones. It has three great moves and a lure option, what else can you ask for?
Sub+Hex Gengar is something that Cicada posted about
here to go with Glare Serperior, and that describes the synergy better than I ever could. Gengar can pressure Chansey and Grass-types, both of which greatly irritate the team otherwise.
Mega Gyarados punishes foes that try to Pursuit-trap Gengar, checks Keldeo and other Fighting-types pre-mega and then Weavile post-mega, lures in bulky Grass-types, and is a great finisher after paralysis is spread. Waterfall felt unnecessary, since the team already has a few ways of beating bulky Ground-types.