Battle Moveset

A Good Special Sweeper Moveset for Attack Form Deoxys would have to be this:

Attacks:

Hidden Power Fighting
Psycho Boost
Ice Beam
Thunderbolt

Items Attached:

Petaya Berry

Preferred Nature:

Timid

Strategy Using Attack Form Deoxys

Well, as you could've guessed, Attack Deoxys has high attack strengths(both have a base of 180). Not only this, it has a base speed of 150, meaning you're going to have trouble hitting Deoxys first.
The moveset is simple, use whatever move you feel will prove more useful to you, maybe have a different HP if you want, but it is Fighting to take out Dark Pokemon. I didn't suggest moves like calm mind or Recover simply because the time it takes to use these moves leaves Deoxys open to attacks, and with extremely poor defenses it won't last long.
Again, the EV's and nature are intended to boost speed. If you want, you could make Deoxys a Physical sweeper too, with moves like Psycho boost, Brick break, Shadow Ball, Return.
Deoxys could be beaten by something that is faster and is a special/physical sweeper, or has the moves Shadow ball/Crunch in its moveset. However, as stated previously, Deoxys speed is something to contend with, and this gives Deoxys an advantage in battle.
Overall, Attacking Deoxys has some of the best stats in the entire game, even though its a legendary, it still has its weaknesses.

EV Corner:

Max out the EVs in Speed & Special Attack for Deoxys with any remaining in HP

Strategy Against Attack Form Deoxys

Attack Form Deoxys has really really weak defenses. Any powerful attack should do serious damage to it...maybe even knock it out. Especially Dark or Ghost Attacks

Contest Moveset

A good Contest Moveset for Attack Form Deoxys would have to be this for the Smart Contest best with Calm, Gentle, Careful, Sassy Nature:

Attacks:

Calm Mind
Psychic
Reflect
Psycho Boost

Items Attached:

Green Scarf

Strategy Using Attack Form Deoxys

If you do the attacks in this following order you should have very few problems; 1st - Calm mind, 2nd - Psychic, 3rd - Reflect, 4th - Psycho boost, 5th - Psychic

Locations in Games

Ruby/Sapphire Not In R/S Colosseum Not In Colosseum Fire Red/Leaf Green Island 9 on Fire Red ONLY

Animé Appearences

Deoxys has had one Animé Appearence. It came from a Meteorite carrying a Golden Egg...however as soon as it crash landed on Earth, it got under attack by Rayquaza. It went into Attack Form to get the most damage against Rayquaza...and when it returned to LaRousse City, it went into this form to attack to find it's missing Crystal Body. Movie 7: Visitor Of The Space Fissure!