Getting all puzzle pieces
Aside from other online functionality, the shutting down of 3ds servers also has shut down Spotpass, which enabled 3ds players to obtain new puzzle pieces. Without Spotpass functionality, it is not possible for 3ds players to even see additional panels that were released after the launch of the 3ds. Following this guide will enable all panels for your 3ds (but you're still left to find the puzzle pieces on your own!).
Additionally, there were several puzzle panels that were special to a specific region. Following this guide will ensure you have all 60 puzzles plus 3 additional Japan-only puzzles. You can also optionally only install either the 60 panels, any of the additional panels, or all of them at once.
Obtaining all panels
- Go to this page and download the correct zip file for your 3DS's CURRENT region (so, if you have a Japanese 3ds but it has been region swapped to EUR, choose Eur.BOSS.zip)
- Open up your Mii Plaza and ensure Streetpass and Spotpass are enabled in Settings
- Copy the contents of the zip file you just downloaded to a folder on your SD card. Simply go to the root of your SD card on your computer and create a new folder called Spotpass Data, then put all the weirdly named files inside from the archive you downloaded.
- Open FBI, select SD, then locate the Spotpass Data folder you just created.
- Press A on the option that says Select Current Directory, then hit Copy All Contents.
- Hit B until you're back in the FBI top menu, then select EXT Save Data.
- You should now have an option called Streetpass Mii Plaza, press A on that, then go to Spotpass Data.
- Press A on the option that says Select Current Directory, then hit Paste. If it asks you to replace files, you can safely say Yes.
- Launch Streetpass Mii Plaza and go to your puzzle game. You should now receive a free puzzle piece for the new panels.
- Note: If you are having issues or it says your data is corrupt, it is probably because you installed the plaza stuff out of order (so, installed the DLC BEFORE installing the Update, which is only possible with a hacked 3ds) in Streetpass itself. If this is the case, you will have to delete all Streetpass data and start over.