Gallade – Adamant Nature w/ Scope Lens - Psycho Cut, Stone Edge, Leaf Blade, Close Combat
basically a Critical happy set.
Lanturn – Modest Nature - Thunderbolt, Surf, Ice Beam, Volt Switch
Volt Switch is fine, but try checking its Hidden Power, just in case it has a usable type that can improve its coverage.
Mamoswine – Adamant Nature - Earthquake, Rock Slide, Ice Shard, Curse
fully physical is the way to go when using Mamoswine. Also, having only STAB move is always a bad idea.
Honchkrow – Mild/Rash/Lonely/Naughty/Hasty/Naive Nature - Aerial Ace, Dark Pulse, Psychic, Thunder Wave/Toxic/Hidden Power/Heat Wave
Aerial Ace is better than Wing Attack due to its accuracy. It may have less PP, but you won't need that many PP anyway. And Aerial Ace has the same base power as Wing Attack, which means there's no power loss either. Heat Wave is preferable for the last move, but it requires B/W 2 move tutor. Hidden Power is usable only if its type is NOT Flying/Dark/Ghost/Poison. There's no need in having both Ghost & Dark move since they share the same coverage.
Giratina - Dragon Claw, Aura Sphere, Shadow Ball, Shadow Force
It's a bit hard to determine the Nature for a Mixed Giratina, since no matter what you'll reduce one of its best stats, the Def/SDef. Unless you're purely using the Origin Forme that is. If it's the Origin Forme, use the same Nature as Honchkrow, if it is Altered Forme, it might be better to use a neutral nature......
Also, it is better to teach it something else instead of Shadow Ball, since Shadow Force already fills the role of a Ghost STAB. You can replace Shadow Ball with one of these : Stone Edge, Energy Ball, Charge Beam, or even Will-o-Wisp.
Arceus – Modest/Timid Nature - Shadow Ball, Thunderbolt, Flamethrower, Judgement
Moveset is fine, just make sure it is holding the Draco/Icicle/Fist Plate. Preferably the Draco Plate.