In just 12 simple steps, you too can control 8 characters at once, thanks to this fantastic glitch:
Have 8 amiibo.
Use a controller that can “desync” (a GameCube controller preferably).
Go to the 8-Player Smash mode.
Just move your joystick until the “Player #” or port space pops up.
Click the name part of your port until it says “None”.
Remove your controller from the port or desync it.
Scan your amiibo.
Plug your s**t back in.
Move your joystick again and now you will be the Player in the next available space after your scanned amiibo. Nothing out of the ordinary, but trust me, it’s working.
Repeat Steps 5-9 until all the Player spaces are filled with the 8 amiibo.
Go to the Settings (where Time or Stock and Item rules are). Then simply exit.
Enjoy controlling 8 characters simultaneously!