Arceus: I love Cosmic Power just as much as you do. But for ExtremeKiller, you need Ghost coverage. Replace it for Shadow Ball. If you wanted, you could replace Recover for Magic Coat, as its your lead, and you hate nasty status... You can mix it up. Either go with Cosmic Power and Magic Coat, or Recover and Shadow Claw. While you're boosting, the opponent will set up on you, so Magic Coat/Taunt is recommended, as you have no spinner. Your item could be changed to Leftovers, as with your current set Silk Scarf would work better anyhow.
Replace Psychic for Psystrike, and if you want you could also replace Thunderbolt for Shadow Ball/Aura Sphere to hit Mewtwo and Deoxys forms or Darkrai and Ferrothorn harder, respectively.
Iron Head doesn't provide any coverage at all for you par flinching, and that shouldn't be used except on Jirachi. Replace it with V-Create or Earthquake.
Nice Lugia. You probably want to replace Recover for Roost, however, to halve that 4x Thunder weakness. Another optional thing you could do is replace Psychic for some status, as it doesn't cover much. Toxic will work well.
Great set! Replace Signal Beam with Shadow Ball for more power. Although, if you want, I have a better Deoxys-A: mixed. It's your choice.
Deoxys-A @ Life Orb
EVs: 88 Atk/168 Sp. Atk/252 Spd
Hasty Nature (+ Spd, - Atk)
- Psycho Boost
- Ice Beam
- Shadow Ball
It's an altered version of your moveset.
Nothing to say; maybe Scarf to outspeed things or Specs to hit hard. Salac Berry? O_o
Overall, great team. You have a lot of special sweepers, however. Mewtwo, Deoxys-A (before I changed it), and Kyurem. Watch out for special walls and Calm Minders (boy, are there a lot of 'em!) and preserve rayquaza.