A Good Deoxys...

[Always and Never]

What is a good way to train a Deoxys?

Like moves, EVs, nature.

And what levels should I switch its forms to get the best stats.

 

[sims796]

Is there a specific form you are talking about?

 

[MegaDitto]

The Attack Dexoys is common in a competitive environment. So it's best to go with that. Grass Knot is a useful attack is the Uber Environment.

Attack Dexoys @ Leftovers/Life Orb
Nature:Lonely/Modest
EV: 252 Speed/ 252 Special Attack
-Grass Knot
-Psychic
-SuperPower
-Substitute

Or

-Psychic
-Super Power
-Ice Beam
-Thunder Bolt