LOL, Über team...

[InterFed_OV]

This is my first attempt at using Legendaries, so please bare with me if the team seems a little n00bish.

Raikou@Leftovers
Pressure
Timid/252 SpAtk/252 Spd/6 HP
-Thunderbolt
-Crunch
-Hidden Power [Grass]
-Calm Mind

Celebi@Leftovers
Natural Cure
Calm/252 SpDef/252 HP/6 Spd
-Psychic
-Leech Seed
-Heal Bell
-Recover

Mewtwo@Leftovers
Pressure
Modest/252 HP/252 SpAtk/6 Spd
-Thunderbolt
-Ice Beam
-Recover
-Calm Mind

Groudon@Leftovers
Drought
Jolly/229 Atk/252 HP/29 Spd
-Earthquake
-Overheat
-Rock Slide
-Swords Dance

Kyogre@Leftovers
Drizzle
Timid/252 HP/229 SpAtk/29 Spd
-Water Spout
-Thunder
-Ice Beam
-Calm Mind

Shedinja@Brightpowder
Wonder Guard
Naughty/255 Atk/255 Spd
-Shadow Ball
-Silver Wind
-Swagger
-Swords Dance

[Absol]

Raikou I think should have CAlm Mind, Thunderbolt, Crunch, and HP:Grass.

Celebi looks alright. maybe some tweaking with the EVs though.

Calm Mind on Mewtwo and a Salac Berry or Leftovers. if you want this for uber games, use Ice Beam, Thunderbolt/Thunder, Recover. Otherwise, go with Psychic, Fire Blast, Recover.

Groudon should be Jolly, with 252 Attack, 228 Spd, and 28 HP. Overheat/Fire Blast over Eruption. Leftovers over Liechi Berry.

Boah isnt good in uber battles. Use Kyogre.
Kyogre@Leftovers
Timid, 252 SpAtk, 228 Spd, 28 HP
Calm Mind
Surf/Hydro Pump/Water Spout
Thunder
Ice Beam

Registeel is also a bad choice. I'll let you choose what to use.

[_-*$carface*-_]

I think Mewtwo should have Psychic, Calm Mind, Fire Blast and Ice Beam.

[MajinRokusho89]

Let's see...

Raikou: Looks pretty good. No complaints.

Celebi: I have no experience whatsoever with Celebi, as I've never owned one (I don't think...I might have Gamesharked one in Gold or Crystal), but this moveset looks pretty good.

Mewtwo: Bolt-Beam Mewtwo is vicious, but I personally always like a STABed Psychic on Mewtwo. However, I don't really think that any change is neccessary.

Groudon: Personally, I don't think Speed is really neccessary to raise here. I'd take the EV's from Speed and swap them with those from Attack. The moveset, however, seems pretty good.

Kyogre: I've always found this moveset to be godly. However, here I have the same EV issue as with Groudon. Speed isn't really all that neccessary on something like Kyogre, so I'd say swap the Speed EV's with the Sp. Attack EV's. With 229 EV's in Sp. Atk, this moveset will really cause some damage.

Shedinja: For nature, go with any nature that hurts Def, Sp.Def, or Sp.Atk to benefit either Attack or Speed. Sp. Atk is pretty much useless, and raising Def or Sp.Def won't do a bit of good. Also, for EV's, go with 255 in Attack and 255 in Speed. Again, HP and defenses mean nothing to Shedinja: if it gets hurt, it dies, no matter how high you make defenses. As for moveset, this one should do fine. Maybe consider Toxic if you think it would work well, but frankly your current moveset seems good enough.

[_-*$carface*-_]

I think Groudon should have Fire Blast instead of Overheat. And Solar Beam instead of Rock Slide for Water Types. Shedinja is good. So is Kyogre. Thats what I think.

[InterFed_OV]

Fire/Ice on Mewtwo is redundant. Fire Blast/Solarbeam on Groudon is bad because Groudon's SpAtk is weak. I would've preferred to keep Eruption on Groudon, though.