The person above is wrong you get on Fire Red, Leaf Green, Ruby, Sapphire and Emerald. I know this for a fact because there are 4 forms of Dexoys which is on the games. Use can use Mystry Gift to copy the Auroura Ticket(the ticket to get to Birth Island) to any of the games.
truthfully, the person right above me is right, (i think). all i know is that u can go into space and catch him in LG, FR and emerald. and im trying to figure out a few things with this too. cuz i accidently got rid of deoxys in diamond.( i know, ouch.) im going nuts over the ppl i got rid of. deoxys, blazican, flygon, blastoise,ect. (BIG ouch.)im trying to find out how 2 catch latios and latias. in sapphire. latias,(i think is the red one?) is in the wild. (im having crap at finding him) and latios( oh i think u know what color. BLUE!) is in southern island( trying 2 figure out how 2 get there.). that's all i have. sry about getting off topic. but u must admit, sounds kinda ouch and interesting. lol. BYE!