Ummm. Arumph! cough this could use some help...
XtremeKiller Arceus-
This guy is never a lead. He is usually for cleaning up the messes left over. (But once I did almost 6-0 a guy with it in the lead.) But other wise this is not a lead. Save him to take out the weakened pokemon at the end.
Giratina-
Good. Not much here except run this nature and EVs: 216 HP/ 56 Def/ 184 SpA/ 52 SpD and Bold nature. This will allow your CM and Sub to have a better effect.
Dialga-
Replace Adamant Orb with Life Orb and Overheat with Earth Power. And Giratina can switch into a predicted fighting type attack while both synergizing and getting a free switch in.
Palkia-
Ok. Too many dragons! Replae him instead with Lugia. And use this set.
Lugia @ Leftovers
Multiscale
Bold
252 HP/ 176 Def/ 80 SpD
Roost
Dragon Tail
Substitute
Toxic
Roost to heal, Dragon Tail to prevent you from becoming taunt bait. Sub well because it is a sub on Lugia. And Toxic cause it is a great status move.
Groudon-
Does not fit on this team. Instead get a lead pokemon on your team. use Forretress.
Forretress @ Shed Shell
Sturdy
Relaxed
252 HP/ 176 Def/ 80 SpD
Spikes
Stealth Rock
Counter
Rapid Spin
Usual set up Tress. Nothing to say.
Mewtwo-
What is with Hardy nature??? Use Timid instead. And give him Life orb over Leftovers. Change out Grass Knot with Psystrike because Ice Beam and Aura Sphere will hit everything Grass Knot does.