
Groudon
Great but you could go with a sweeper set: Adamant; 252 Attack, 140 Speed, 118 Hp; Earthquake, Rock-polish, Stone-edge, Fire-punch.

Starmie
Great special sweeper and rapid spinner but you may want to consider, provided you do not mind losing a rapid spinner, going with Shaymin Sky form as your special sweeper.

Item: Focus-sash
Ability: Serene-grace
Nature: Timid
EVs: 252 S.Attack, 252 Speed, 4 Hp
Growth: Boosting
Seed-flare: STAB+Lower S.Defense
Air-slash: STAB+Flinch
Earth-power: Coverage
Shaymin with be hitting extremely hard after just one Growth as it boosts S.Attack(and Attack but it is not important here) by 2 stages.

Ho-oh
While I understand that you are trying to lower your opponents speed with Bulldoze you should really use Earthquake instead, it is far stronger as you know and honestly you could KO the Pokemon with it in the time you take to lower its speed.

Reshiram
Amazing no suggestions.

Shedinja
I know he is good in ubers but quite honestly he does not provide this team with anything important. I would switch it for a Pokemon that can counter Kyogre. Maybe Mewtwo if you do not mind another special Pokemon or Zekrom if you do. The sets should be:

Item: Choice-specs
Ability: Pressure
Nature: Timid
EVs: 252 S.Attack, 252 Speed, 6 Hp
Aura-sphere: Coverage
Grass-knot: Coverage
Ice-beam: Coverage
Psystrike: STAB Kyogre Killer
Pystrike will 2KO Kyogre I ran the stat calculations.

Item: Choice Scarf/Band
Ability: Terravoltage
Nature: Jolly
EVs: 252 Attack, 252 Speed, 6 Hp
Bolt-strike: STAB+Kyogre-killer
Dragon-claw/Outrage: STAB
Stone-edge: Coverage
Crunch: Coverage
Bolt-strike will OHKO Kyogre even without Choice-band, I ran the stat calculations.

Arceus
Amazing no suggestions.






Overall team
The team is pretty good but it lacks counters to get rid of Sun counters, but if you use the suggestions it will be an amazing team.