For those who didn’t know, the Mewtwo DLC is out and ready to be downloaded for those who purchased and registered both versions of Super Smash Bros. Unfortunately, things are not all good. Apparently with the DLC came glitches.
If you use Mewtwo in 10-man Smash on the Wii U, it locks you out of online multiplayer. You can also encounter this bug if you use Mewtwo in Classic, All-Star, Stadium, Trophy Rush, or Smash Run on 3DS.
The good news is Nintendo knows about this and is working on a patch now. Until then, it’s recommended that you don’t use Mewtwo in these modes and just play regular Smash, Smash Tour, or just play online.