Instructions
Attend one of Nintendo's official Pokemon events, either through a Wi-Fi connection or in a store. You can find recent event listings on the official Pokemon website's "News and Events" page or on the Serebii.net event database. Bring your Nintendo DS and your copy of "SoulSilver" to the event to receive Deoxys.
Trade for Deoxys from other Pokemon games. In "Emerald," "FireRed" and "LeafGreen," you will find Deoxys on Birth Island after a player attends a Deoxys event for those games. The player must follow a black triangle around the island in as few steps as possible before battling and capturing Deoxys. Save after Deoxys is captured and turn off the system.
Insert "FireRed," "LeafGreen" or "Emerald" into the Game Boy Advance port on the Nintendo DS, if you have not already done so. Insert "SoulSilver" into the Nintendo DS port on the same system.
Turn the system on. On the main menu, scroll down until you see the option to transfer Pokemon from "FireRed," "LeafGreen" and "Emerald" through Pal Park. You will then capture Deoxys again without a battle.
Save your game and turn off the Nintendo DS.