This will be simple because I'm short on time, I'm just going to fix your sets for now but if I have time later I'll fix the synergy too.
Genesect:
Genesect @ Choice Scarf
Trait: Download
EVs: 252 Atk / 252 Spe / 4 SAtk
Hasty Nature
- U-Turn
- Iron Head
- Ice Beam
- Flamethrower
Darkrai:
Darkrai @ Life Orb
Trait: Bad Dreams
EVs: 252 Spe / 242 SAtk / 4 Def
Timid Nature
- Dark Void
- Nasty Plot
- Dark Pulse
- Focus Blast
Arceus-Steel (I did change Arceus because you needed a Kyogre check):
Arceus-Grass @ Meadow Plate
Trait: Multitype
EVs: 96 Spe / 248 HP / 164 SDef
Timid Nature
- Judgment
- Defog
- Will-O-Wisp
- Recover
Blaziken:
Blaziken @ Blazikenite
Trait: Speed Boost
EVs: 252 Atk / 252 Spe / 4 SDef
Adamant Nature
- Swords Dance / Protect
- Low Kick
- Flare Blitz
- Knock Off / Stone Edge
Up to you whether or not you want the Protect for Speed sweeper or Sword Dance for the more suicidal killer. Stone Edge or Knock Off depending on whether or not you have issues with Ho-Oh or not.
Xerneas:
Xerneas @ Power Herb
Trait: Fairy Aura
EVs: 252 SAtk / 120 Spe / 136 HP
Modest Nature
- Geomancy
- Moonblast
- Hidden Power [Fire]
- Thunder / Substitute
Giratina:
Giratina-A @ Leftovers
Trait: Pressure
EVs: 248 HP / 252 Def / 8 SDef
Bold Nature
- Rest
- Will-O-Wisp
- Sleep Talk
- Dragon Tail
That should help a little, I'll come back and try to improve your team more when I have more time or a better computer.
Cheers.
