Edge running glitch
The edge running glitch is a glitch in Super Smash Bros. Brawl, Super Smash Bros. 4, and Super Smash Bros. Ultimate which allows a character to run against a platform's edge without falling off. The method of doing it has changed between games. Prior to Ultimate, it involved running towards an edge and holding the control stick in a particular fashion before arriving. While it can be done simply by relaxing the stick towards the neutral position, it is slightly easier to accomplish by rotating the stick into a diagonal position (without going far enough to input a jump or crouch), allowing a reduced sideways input while still holding the stick against the edge of its well. The glitch works because the "amount of tilt" required to move off an edge is higher than the "amount of tilt" necessary to maintain a run once it has begun. The more complicated a platform is, the harder it is to perform the edge running glitch, and as a result, it's the hardest to do this glitch on slopes like Yoshi's Island.
It has very few uses, as maintaining a running state means that the player cannot use the majority of their attacks, and it can be tricky to maintain for a period of time. Its only potential usage (aside from simple mindgames against opponents unaware of its existence) is in surprise usages of powerful dash attacks (such as King Dedede's) on opponents that are recovering overhead. The glitch cannot be done if there is a ladder under the edge. The character will use the ladder instead.
In Ultimate, the method of performing it has drastically changed. It now must be executed by holding both the A and B buttons (which normally is used to execute smash attacks) while a character is doing their turn-around animation. Due to this change, characters can run at a faster speed than in prior games while performing the glitch. Due to the turnaround frames increasing drastically while skidding on ice terrain, it is much easier to perform on stages with this kind of terrain. It also now has some more potential usage, due to the mechanic of being able to use more attacks out of a dash.