List of Super Smash Bros. Ultimate glitches
From the Super Mario Wiki
This is a list of glitches in Super Smash Bros Ultimate
Note: All names are conjectural unless otherwise specified.
Indefinite Assist Trophies
To use this glitch, both the player and at least one opponent has to be playing as Isabelle. Then, they need to wait for an Assist Trophy to appear, and both grab it with their Fishing Rod special move at the same time. If done correctly (with one character reeling it in while the other's line is still attached), the player who successfully reeled in the Assist Trophy will continuously keep spawning copies of the character until they get hit, pushed into a blast zone or KO'd.
This does not work with a few Assist Trophies (like the Squid Sisters) and does not spawn in clones of a few others (like the Moon from The Legend of Zelda: Majora's Mask).
The glitch can also be done with other items too. If the player does the same thing with a Warp Star, they'll be trapped and unable to attack damage, whereas doing the same trick with a Hammer causes it to do no damage and removes the effect of the lower blast zone.
As of the version 2.0 update, this glitch has been patched.
This glitch turns playable characters, Assist Trophies and items into shadows, reminiscent of Dark Link from Super Smash Bros. Melee. To use it, the player needs at least one third party controller without gyro/motion control functionality, and to pull off one of the two methods outlined below:
The Original Method
Then simply press down again to activate the glitch.
The Simplified Method
If done correctly, everything will turn black and the glitch will be activated.
As mentioned, this will turn all characters, assist trophies and items into shadows, while leaving backgrounds and stages untouched.
For this glitch, the player has to use either Villager or Isabelle, with their opponent using the other character. Then, they need to use their Slingshot special attack on their opponent, and their opponent needs to catch it with Pocket. Once that is done, if the other player releases the Slingshot attack afterwards, the game will crash.
This glitch has been patched as of update 2.0
Gale Stab Crash
If the player uses a Mii Swordfighter with the following moveset:
This glitch has been fixed in version 2.0.
Joker Classic Crash
In Joker's Classic Mode, if Joker finishes a battle with his Final Smash, the game will crash. This is because Joker's Final Smash usually creates a separate victory screen if he ends with his Final Smash, however, the screen doesn't appear in Classic Mode.
Piranha Plant Single Player Data Corruption
If the player plays as Piranha Plant on a digital copy of the game, then sets a record in All Star Smash, there's the possibility the game will crash and erase all the save data. This has also been reported in other single player modes like Classic Mode, and may come from the game not expecting an additional character to have data associated with it.
Century Smash Data Corruption
If the player throws Pikmin at an opponent's Mother Brain Assist Trophy as Olimar, the Pikmin will grow in size along with Mother Brain. However, these giant Pikmin are only different on a cosmetic level, and will return to normal size once they either fall off Mother Brain or Mother Brain vanishes.