Deoxys

 How to Obtain 

You can get Deoxys by having Lunatone and Solrock (both found at Victory Road) in your party and going to the green Pichu patch at Mysterious Grotto. When you have found Deoxys, it will say "Your Solrock and Lunatone were noticed by something! Deoxys attacked!"

 Forms 

There are 4 Forms of Deoxys, depending on which meteorite you change it to. (Regular, Attack, Defense, Speed).

You can change its form at anytime, but not during battle. (Go to one of the four Meteorites, there is one Meteorite for each form, then click on the preferred one then search for Deoxys in Pichu Grass Patch)

Special Move: Psycho Boost (lowers Sp. Attack Harshly)