Adamant Orb is favored over Choice, as it makes a great bluff. Dragon Pulse and Roar Of Time don't go well together, replace the latter for Earth Power to hit other Diagla. You don't need HP Fire when he can use Flamethrower, replace HP with that. If you want to, you could replace Ice Beam for Aura Sphere to cover some different Pokemon. Otherwise, good!
From what I'm seeing, this guy is pretty much a mixed sweeper. I think you should try a different set, E-Quake has meager coverage for taking up a precious moveslot and won't do much with the Evs anyhow.
You'll need to replace Mild with Modest. Now he's an all-out special sweeper. Put all EVs in Sp. Atk and Spd, and put the last four in HP. Now, Judgement (Ice) beats Ice Beam, so use that. Dark Pulse is nice, but replace E-Quake with Focus Blast or HP fighting.
Make the item Wise Glasses, or expert Belt. You already have Bad Dreams, the foe might wake up, no point in Dream Eater and Nightmare! Use Nasty Plot and Thunder instead. Timid nature, and special sweeper EVs.
A special sweeper is getting repetitive. Make the EVs 252 HP, 252 Defense, 4 Sp. Defense.
Replace Ice Beam for Calm Mind. Now you have a wall. Make Bold Nature as well.
try a Scarfed Sweeper. Use a scarf (obviously), and replace HP Fire for Stone Edge. Use a Adamant nature. Replace dragon Claw with Outrage.
why do you have the physical moves, when you have no EVs? Make an Adamant nature, and replace HP Ice with Shadow Sneak. Psychic should go for Toxic or Will-o-Wisp.
New Importable:
Dialga @ Adamant Orb
Trait: Pressure
EVs: 252 HP / 252 SAtk / 4 Spd
Modest Nature (+SAtk, -Atk)
- Earth Power
- Flamethrower
- Dragon Pulse
- Ice Beam
Arceus (Arceus-Ice) @ Icicle Plate
Trait: Multitype
EVs: 8 HP / 248 SAtk / 252 Spd
Modest Nature (+SAtk, -Atk)
- Focus Blast
- Dark Pulse
- Ice Beam
- Recover
Darkrai @ Wise Glasses
Trait: Bad Dreams
EVs: 252 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Dark Void
- Nasty Plot
- Thunder
- Dark Pulse
Kyogre @ Leftovers
Trait: Drizzle
EVs: 252 HP / 252 Def / 4 SDef
Bold Nature (+Def, -Atk)
- Thunder
- Hydro Pump
- Substitute
- Calm Mind
Zekrom @ Choice Scarf
Trait: Teravolt
EVs: 8 HP / 248 Atk / 248 Spd
Adamant Nature (+Atk, -SAtk)
- Bolt Strike
- Crunch
- Outrage
- Stone Edge
Giratina (Giratina-O) @ Griseous Orb
Trait: Levitate
EVs: 200 HP / 56 Atk / 252 Def
Adamant Nature (+Atk, -SAtk)
- Shadow Force
- Dragon Tail
- Will-O-Wisp
- Shadow Sneak
