You can check out the bug being showcased below:
As you can see the bug is very simple to pull off however it is not clear what is causing the game to crash here however your Mii Fighter will require a very specific moveset.
Check out the explanation from FlamingOranges below:
Neutral Special: Shuriken
Side Special: Gale stab
Up Special: Stone Scabbard
Down Special: Reversal slash
Even though you only use the side special, the glitch only worked with all four.
After that’s done, start a match and have duck hunt use his gunman. Once the gunman is out, at any time before or after the bullet fired, or maybe even during, the mii swordfighter gets close to the gunman and uses his side special. Then the game crashes. It’s incredibly easy to pull off, and this was found through normal play.
The glitch seems very easy to pull off and something fun to do with friends however we recommend not doing this in the online mode as it could result in your account being banned.
If we have any more information to share we will cover it here at NintendoSoup so stay tuned for more!