Multiple player slot glitch
The multiple player slot glitch (popularly known as the Ice Climbers glitch and the amiibo glitch in Smash Wii U only) is a glitch in Super Smash Bros. for Wii U and Super Smash Bros. Ultimate. The glitch allows for multiple player slots to be controlled by a single controller, creating an effect similar to the Ice Climbers.
In normal play, a given controller can only be controlling one player slot (such as P1, P2, etc.). Through an oversight on the character select screen, this glitch allows a controller to control multiple different player slots. The result of this is that several "players" in a match can perform the same input at exactly the same time, due to registering inputs from the same controller. They otherwise are completely independent from each other.
The glitch can be performed in any mode that allows amiibo Figure Players: Smash, Special Smash, or 8-Player Smash. It can be performed for several controllers, allowing different sets of player slots to be controlled by different controllers. Team Battles can also be played under the glitch's effects, allowing players to prevent their controlled player slots from hitting each other, similarly to the Ice Climbers.
While performing the glitch, the player can make the character-selection cursors overlap by moving them to the edge of the screen, and in a battle, they can overlap the characters by rolling to the edge of the stage. This can lead to some interesting effects with moves such as Luigi's Super Jump Punch.
Despite the removal in Ultimate, this glitch returns with the addition of patch 3.0.0. However, this method only works in Stage Builder test mode, and the instructions for this glitch is different.
How to perform in Smash 4
After performing these steps, the controller used will be controlling all player slots that it occupied. This can be performed with multiple controllers, allowing the different controllers to control different sets of player slots.
How to perform in Ultimate
A variation of the glitch is present in Ultimate, but cannot be used in actual versus matches and only works with 2 characters.
After executing the glitch, the second controller should control the first player in the stage.
When a controller is disconnected on the character select screen, this normally leaves that player slot present, but open so that the next controller to enter will occupy it. However, when the controller is disconnected while the slot is set to "None", it is possible to scan an amiibo Figure Player to occupy that slot, which does not clear the game's impression that there is still a controller tied to the slot. After re-entering the character select screen by exiting the Rules screen, the game refreshes the state of the player slots, and links the controller to the slots that were occupied by the Figure Players, because they were still flagged as having a controller tied to them.
In Ultimate, it no longer happens as disconnected controllers will remove the player slot even if the controller is occupied by the amiibo, rendering incapable of performing the glitch.