Instructions
Complete the game's story mode; this consists of ten missions. You can only access the Ranger Net, and therefore the extra and special missions, once you have completed the story mode.
Save your game once you have completed the story mode. Go to the game's main menu screen. A new option, the Ranger Net, will appear in the menu.
Select the Ranger Net. Allow the game to identify your Wi-Fi connection.
Choose the extra or Special Mission that you want to embark on; there are three extra missions and three special missions. Wait for the mission to download, then play through the mission in order to encounter new Pokemon.