The infinite Assist Trophy Glitch was a glitch in early versions of Super Smash Bros. Ultimate that caused Isabelle to repeatedly summon Assist Trophies, with no control over this action until she got hit.
In order to perform the glitch, two players must be playing as Isabelle and use Fishing Rod at the same time to grab on to an Assist Trophy. If the glitch is performed correctly (one Isabelle will reel in the Assist Trophy while the other's line is still hooked onto it), the player that grabbed a hold of the Assist Trophy will continuously summon that Assist Trophy until they get hit, pushed into a blast zone, or the animation is cancelled in some other way. Surprisingly, there have been very few recorded instances of the game crashing while this glitch is being performed despite the massive amount of objects on screen, especially with larger Assist Trophies like Rathalos. However, there are certain Assist Trophies that cause framerate issues during the glitch, usually due to generating lots of visual effects and utilizing randomness that the game needs to process all at once. If one player is significantly farther or closer to the Assist Trophy than the other player, the glitch will not work. Additionally, certain Assist Trophies do not spawn more than once, such as the Squid Sisters, instead the summoner will continuously perform the summon animation with no Assist Trophy appearing.
The glitch also works with a handful of other items: for example, Warp Stars will cause the player who picked it up to be stuck grabbing on to it, and no attacks will damage them, while Hammers or Golden Hammers will function as normal but will deal no damage, and the player will not be KO'd by the bottom blast line. The only way to get rid of this glitch is by hitting the player summoning all the assist trophies or resetting positions if the glitch is done in Training Mode.
The glitch was patched with update 2.0.0.
