Cheat to get the aurora ticket then go to birth island.
There are sadly no special events to catch Deoxys in Sapphire. You HAVE to trade a Deoxys caught in an event from FireRed, LeafGreen, or Emerald.
You catch deoxys at birth island.
Go to birth island.
you have to get it in a event and you cant get it in Pokemon leafgreen or firered
Get a Deoxys in Pokemon Emerald, Ruby, Sapphire, Firered, or Leafgreen using the Mystery Gift, and migrate it to your Diamond Version.
Yes you can trade leafgreen version Pokemon to another leafgreen version.
Deoxys cause you can't get it.
You don't get a Shiny Deoxys from a man. You'll need to get Deoxys in Pokemon FireRed, LeafGreen, or Emerald. It is extremely hard to get a Shiny Deoxys.
You can't find one you need to trade one from FireRed/LeafGreen/Ruby/Sapphire or Emerald
You need to migrate it from FireRed, LeafGreen, or Emerald. But if you have a Deoxys in Pokemon Ruby or Sapphire, then you can migrate from them to Pal Park.
Go to birth island.
in a island with mistery gift