Catch Deoxys in FireRed and LeafGreen
1. Go to any friendly Poke Mart
2. On the desk, there should be a small square "memo".
3. Press the a button near the memo and a questionnaire will pop up.
4. Enter the words "LINK TOGETHER WITH ALL".
5. The counter person will react- and tell you that you should now recieve Mystery Gifts!
6. Save your game, then turn off your Game Boy Advance.
7. Turn on your game, and Mystery Gift should appear below the new game slot.
8. When selecting Mystery Gift, you'll see Wonder Gift and Wonder News. Select Wonder Gift.
9. Now you can receive the Aurora Ticket from an authorized Aurora Ticket station (Pokemon Rocks Amrecia, or retail stores to be determined).
10. Go to the 2nd floor or any Pokemon Center in the game.
11. Talk to the man in the green hat.
12. After speaking to him, your Aurora Ticket will be in the Key Items pocket of your bag.
13. Save your game, then turn off your Game Boy Advance.
14. The Aurora Ticket cannot be traded or transferred.
15. Go to the port in Vermilion City.
16. When you speak to the sailor at the dock, Birth Island will appear as a new destination.
17. You must have the Rainbow Pass.
18. In order to obtain the Rainbow Pass, you must first give the Ruby to Celio on One Island.
19. Travel to Birth Island. SAVE YOUR GAME HERE! You will see a large patch of ground shaped like a triangle. A smaller triangle rests in the middle.
To catch Deoxys, you must solve the Birth Island puzzle. Here's the answers:
1. Approach the mysterious triangle from below and press the A button.
2. Press left on your directional pad 5 times, the press down 1 time. Now press the A button.
3. Press right on your directional pad 5 times, then press up 5 times. Now press the A button.
4. Press right 5 times, the press down 5 times. Now press the A button.
5. Press up 3 times, left 7 times, and then press the A button.
6. Press right 5 times, then press the A button.
7. Press left 3 times, down 2 times, then press the A button.
8. Press down 1 time, the left 4 times. Press the A button.
9. Press right 7 times. Press the A button.
10. Press left 4 times, down 1 time, and press the A button.
11. Press up 4 times, then press the A button.
1. Now you can get Deoxys! If you still have the Masterball I suggest you use it, otherwise it's gunna be one tough battle!
Note : I (Sarah) have not tested this theory of catching Deoxys (seeing I cannot get the Aurora Ticket) so I cannot guarantee anything.
Credit : All credit goes to alkutah.