Zero gravity glitch
The zero gravity glitch refers to a glitch in Super Smash Bros. Melee, Super Smash Bros. Brawl and Super Smash Bros. 4 that causes a character to be pressed against a ceiling and appear to float. The glitch is easiest to perform in Hyrule Temple in Training Mode, or on a custom stage with a very low ceiling (the player must be at very high percentages, preferably 999%). It is easiest to perform if player 1 is Peach (or any other character with an attack that causes them to bounce). Peach stands under a solid ceiling (for example, in the lower left part of Hyrule Temple). The target character(s) stand(s) in front of Peach. Peach then uses her down tilt repeatedly. While the game reacts normally by having the target(s) rocket upwards and then bounce downwards, after a few rounds, the target(s) stick(s) to the ceiling in their falling state.
The glitch likely happens because of the character travelling so fast that the game doesn't realize he/she/it needs to bounce off the ceiling, and instead keeps traveling upwards, sticking to the ceiling. Since the character is in their falling state, they can use any aerial moves. However, since they are still traveling upwards at tremendous speed, moving sideways to a point without a ceiling will probably KO them. Waiting for around 20 seconds will cause the character's momentum to fade, eventually allowing them to fall. Moving away from the ceiling when momentum is getting low may fling the character upwards, but not enough to KO them.