Ruby/Sapphire E-Reader Events
Trainer E-cards
In Ruby/Sapphire you can scan some special e-cards that contain trainers and they will appear in your game. In order to use the e-reader, go to Petalburg's Pokémon Center and talk to the man near the PC. He will allow you to change your profile and you must put "MYSTERY EVENT IS EXCITING". He will then tell you that you know the secret saying and that you must be a member of the Mystery Event Club. Now save your game and go back to the menu screen, connect your Game Boy Advance with another Game Boy Advance that has the E-reader on it, and then select MYSTERY EVENT. After you have finished with that, go to Mossdeep in an old man's house, there you will be able to fight the trainer from the e-card. It will be a 3 on 3 battle and items are not allowed. Check the screenshots below for visual details:
This is how you properly connect the E-reader.
This is a Trainer e-card.
This is what E-reader's screen should show. This is what your game should show.
This is the place you finally battle the trainer.