Summarize the following:
If you accidentally released Latias by answering "Red" when you talk to your mother, the only way you can legitimately find Latios is by trading for it. You can use Gameshark codes if you are using an emulator and don't have someone to trade with (see the next steps). The Eon Ticket was a special event item that was distributed to players, which allowed players to access a special island where they can catch Latios or Latias, depending on which one they released. Since the ticket is no longer available, you'll need to use cheat codes to get it. To use Gameshark codes, you'll need to be using an emulator like Visual Boy Advance. While there are codes to get Latios directly, it's recommended that you use the ticket instead. When you add Pokemon using codes, they can be fairly buggy, so use the ticket instead and catch the Latios as the game expects you to. This will also make the Pokemon legitimate for tournaments, as it is not a hacked Pokemon. In order to successfully use the Eon Ticket, you'll need to enter a code for both the ticket and the event. You'll also need to enter two Master codes, making four codes total that will need to be entered. Make sure Pokemon Emerald is running and click the "Cheats" menu. Select "Cheat list..." and then click Gameshark... to enter a new cheat code. Enter the following codes, creating a new code for each separate box. Enter the "Description" into the "Description" field, and then copy the code into the Code field. Description: Master D8BAE4D9 4864DCE5 A86CDBA5 19BA49B3 Description: Anti-DMA B2809E31 3CEF5320 1C7B3231 B494738C Description: Eon Ticket 121F112F DA7E52B4 Description: Southern Island 0D6A02AA B44948BD After entering all of the codes, restart Pokemon Emerald and go to your PC in the game. You should be able to find the Eon Ticket in Slot 1. Withdraw it from the PC and add it to your inventory. When you're holding the ticket, you'll be taken to Southern Island instead of Slateport City. Once you're on Southern Island, you can fight Latios by using the sphere at the center of the island. Latios won't try to run in this fight, so use the techniques outlined above to wear it down and capture it.

Summary:
Trade for Latios. Use Gameshark to get an Eon Ticket. Enter the codes for the Eon Ticket. Retrieve the Eon Ticket from your PC. Take the ship from Lilycove City Harbor. Fight Latios.