You have to do somthing with all three games.
deoxys can be found on birth island only by having the aurora ticket.
Yes if you have an aurora ticket.
It is not possible to get Deoxys without the Aurora Ticket for you can only find it on Birth Island.
Aurora ticket is only avaible in leaf green, fire red and emerald. But not ruby or sapphire.
use the mystery box if you have it and then you'll have the ticket
No, not unless you have obtained the Aurora Ticket from a Nintendo Event and captured Deoxys in Fire Red, Leaf Green, or Emerald. You can also obtain an Aurora Ticket using a cheat code, but that is not good way to get it. If you have captured Deoxys on Fire Red, Leaf Green, or Emerald, you can migrate it to the Pal Park on your Pearl version.
The Aurora Ticket was only obtainable if you went to some Nintendo event several years ago; sorry, no longer possible. :(
special event
Do not cheat just find a friend with the mystic ticket and a mystery gift and bam you get mystic ticket
you really can not get deoxys in Pokemon ruby but you could get a gameshark and hack and i think you need aurora ticket
you have to get the aurora ticket from a Pokemon event in japan. then you give the ticket to the ferry person and he takes you to Birth island.
You half to go to a Nintendo event or use a cheat device.