first fly to the lost ruins and stand there for five seconds and one will pop up
you can get him in a trade from GTS or use AR OR you can get him in a event.
You can use the GTS :P
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You can't :'(... you have to use cheats, trade from diamond or get it in the GTS! if you need to see it battle the couple in the lost tower
you use the global trade system
You would need to use an Action Replay or transfer it from Pokemon Emerald, FireRed, or LeafGreen, for it is impossible to catch Deoxys in any location in Pokemon Diamond, Pearl, and Platinum.
You could have gotten an event deoxys in Gamestop when Pokemon Diamond and Pearl came out, but it is over and there is no way you can get a deoxys unless you trade or use an Action Replay. Sorry.
You can't. The only ways you can get a DEOXYS in Diamond are you hack, use an action replay or game shark, or you migrate one from Hoenn and catch it in pal park. Good day to you.
On the game when you complete it (defeat N, ect) you can go to route 15, theres a place there where 2 DS's can comunicate to trade.. BUT you can trade Pokemon from Pokemon Diamond, Ect Ect. Or you could just use GTS trade in the Pokemon centres. :) Hope i helped!
you can't its only in pearl and platinum you could use GTS or migrate your Pokemon from ruby,sapphire or emerald
I use Ho-oh arceus darkrai jirachi groudon and deoxys
You can't you just have to migrate it or use Action Replay P.S you spell it like Diamond...