Pokemon Emerald for GBA:

How to get a legitamate Deoxys that will not cause you to:

a: glitch or ruin your GBA game
b: make you loose all your Pokemon
c: restart your game
d: schedule vacation time and drive 400+ mile to the Manhattan Pokemon Center

What you need:
-Game Boy Advance
-GBA Pokemon Emerald cart that is saved after you have beaten the Elite 4
-Action Replay MAX for GBA/DS (Yes, I know I said legit, but bear with me)

If you follow these steps to the letter, you will get a legimate and legal Deoxys with out damaging or corrupting your GBA Pokemon Emerald game.

Phase 1: Preparing your in game character.
1. Insert your  Pokemon Emerald cart directly into your GBA.
2. Once in your game;
    -Make sure you have lots of your prefered type of Poke'balls with you.
    -Make sure you have Pokemon in your party that are atleast level 50.
    -Make sure Pokemon in your party know FALSE SWIPE and SING (SLEEP POWDER will work in place of SING).
    -Go stand outside of the FERRY DOCK,  --- DO NOT GO IN!
    -SAVE your Pokemon Emerald game.

Phase 2: Use of the Action Replay MAX
1. Insert your Pokemon Emerald cart into the Action Replay MAX
2. With the power to your GBA turned OFF, insert the Action Replay MAX into your GBA
3. Turn the power ON
4. You should get the Action Replay MAX screen. If you do not, turn off the power, wait 10 seconds, remove the Action Replay MAX and Pokemon Emerald cart and try again.
5. ADD the following code into the Action Replay MAX  after confirming that you are indeed using Pokemon Emerald.
     -Name: Birth Island (Deoxys)

6. After entering the code. Select it to be active (check box icon)
7. Make sure the only other active (checked) code is the " (m)  "  default code
8. Press "START" on the GBA
9. Your Pokemon Emerald cart should boot with in 20 seconds. If it does not go back to step 2.
10. Load up the game you saved in Phase 1.
11. You should be in LILYCOVE CITY in front of the FERRY DOCK.
12. Enter the FERRY DOCK
13. You will be exit onto a ferry dock at the bottom of a small triangle shaped island.  The little drop down sign on your GBA should say "BIRTH ISLAND"
14. SAVE YOUR GAME!!!  Do NOT move or do anything else, just SAVE your game.
15. After your game save is complete, wait 5 seconds then turn OFF the power to your GBA.
16. Remove the Action Replay MAX from your GBA.
17. Remove the Pokemon Emerald cart from the Action Replay MAX
18. You will no longer need the Action Replay MAX after this.
19. Reinsert the Pokemon Emerald cart directly into your GBA. 
Phase 3: Going after Deoxys
1. Power on your GBA with the Pokemon Emerald cart installed.
2. Load up your game to the last save.
3. You are still on BIRTH ISLAND. The now disconnected Action Replay MAX did not alter or damage any of your game or Pokemon. It simply allowed you to go to BIRTH ISLAND one time as if you had downloaded the ticket wirelessly at a Nintendo event. You will first notice that there is no music. Your GBA [SP] isn't broken or glitched, so don't freak out. There is no music in this part of the game. It has that eerie quiet thing going for it.
4.  You'll see a triangle-shaped plot of land and a dark grey triangle in dead center. Your job is to manipulate the movements of this triangle so it ends up one square above center, getting it to turn red instead of dark grey. As long as you don't turn unnecessarily (you have to start over if you turn even once out of line), you can simply walk to the triangle as it moves.
5. When you touch the triangle, press "A" to move it to another location.
    -Start at the bottom of the triangle.
    -One step down and all the way left.
    -Three steps right and all the way up.
    -Five steps down and all the way right.
    -Three steps up and all the way left.
    -All the way right.
    -Two steps left and all the way down.
    -One step down and all the way left.
    -All the way right.
    -Three steps left and face down. This will make the triangle turn red and one square above center.
6. SAVE NOW!!!
7. Walk to the triangle and press "A" one last time. The ground will shake and the triangle explodes. Deoxys will descend and attack.
8. Deoxys is Level 30, and just like other legendary Pokemon, if you K.O. Deoxys, he's gone forever.  (Good thing you saved previously, RIGHT?)<>
9. After capturing Deoxys you are done on BIRTH ISLAND. (There are no other Pokemon or items there.) Speak to the sailor to return to LILYCOVE CITY.
10. Once in LILYCOVE CITY exit the FERRY DOCK.

You now have Deoxys ! If you had less than 6 Pokemon in your party, he will be in your party. If you had 6 Pokemon with you, he will have been transported to the appropriate box on Lanette's PC.

The Deoxys you have caught is the real deal. Just like you would have gotten had you driven to Manhattan to download the wireless ticket. He is not an Action Replay glitched Pokemon. You only used the Action Replay to get to BIRTH ISLAND. Your Deoxys is the real Nintendo authentic deal!