Some Super Smash Bros. Ultimate players have recently discovered that one of Joker's attacks can softblock the game.
When Joker from Persona 5 was announced as the first paid DLC character for Super Smash Bros. Ultimate, there was only a brief animated segment showing him in action. It contained no gameplay footage, so fans began to speculate about his moveset.
The most obvious move choice for Joker was that his Final Smash would be the All-Out Attack from Persona 5, which involves all members of the Phantom Thieves on the field attacking the enemy at once and ends with an image of Joker pulling his sleeve, with the text "The Show's Over" written on the of the screen. Joker is now available to download and his Final Smash is indeed the All-Out Attack and even includes the shot of Joker at the end.
It seems that Joker may have been taking his own Final Smash's text a little too seriously, as it's actually possible for him to end the show by softlocking the game.
Fans on websites such as Reddit are complaining that Joker's Final Smash is freezing Super Smash Bros. Ultimate during the moment when it shows the Persona 5 artwork, forcing the player to reset the game. There have also been complaints about the issue being made on the Nintendo Support Forums.
The softlocking issue seems to occur during Joker's run in Classic Mode, where the player has to battle shadow-themed enemies and turn them into allies. As of the time of writing, there doesn't appear to be any kind of workaround other than just not using Joker's Final Smash in Classic Mode.
Super Smash Bros. Ultimate has had a few nasty bugs since launch, such as Pirahna Plant potentially wiping the save file of the game and a battle between Duck Hunt & Mii Swordfighter causing the game to crash. It has been theorized that Super Smash Bros. Ultimate was rushed out the door to meet the 2018 holiday deadline and the presence of these bugs seems to confirm that the game wasn't fully tested before launch.
Joker is available to purchase for Super Smash Bros. Ultimate right now - just be careful about using his Final Smash in Classic Mode.