Instructions
The Aurora Ticket
Attach an Action Replay device to your Game Boy Advance. Insert the Pokemon Emerald game into the device and turn on the console.
Enter the following master code into the Action Replay device when prompted: 9266FA6C97BD 905B5ED35F81 B76A68E5FAB1. This will allow you to enable additional Pokemon Emerald codes.
Enter this Aurora Ticket code into your Action Replay device: 483511F5 E6C8E537. Begin your Pokemon Emerald game.
Go to any Pokemon Center in the game. These centers feature a red roof and are located in every town in Pokemon Emerald. Access the first floor of the center to the right of the main desk.
Confirm the receipt of the Aurora Ticket at the Pokemon Center and it will be added to your Key Items. You will now have access to Birth Island.
Reaching Birth Island
Travel to Lilycove City. You can reach the city by heading to the northeast section of Hoenn. Lilycove borders the coast with the sea to the east of the city.
Go to the S.S. Tidal, a ferry docked in the southeast of Lilycove City. Speak with the ferry master and choose your Aurora Ticket when asked if you have a special ticket. You will be transported to your cabin on the ferry.
Explore the ferry and battle other trainers or select ̶0;Sleep̶1; in your cabin to head directly to Birth Island.
Leave the S.S. Tidal and you will find yourself on the triangle-shaped Birth Island, where you can find and capture Deoxys.