The yo-yo glitch refers to a glitch in Super Smash Bros. Melee done using Ness's yo-yo. It can be used to attack or grab with near limitless range or attach certain single-hitbox attacks to Ness's body. The discovery of the glitch was a collaborative effort between VilNess, LonelyNess, and Dan Smith, and was spurred on by an innocuous video of an unknown Japanese player accidentally dropping a yo-yo hitbox.
The glitch can be performed in all versions of Melee.
Ness's up smash consists of 3 states each with its own hitbox: outreaching, spinning, and swinging. The yo-yo glitch drops the last hitbox of the up smash onto the ground and leaves it there until Ness gets KO'd or uses a non-projectile attack. Opponents can get hit by a dropped yo-yo hitbox or a jacket exactly once. Additionally, if an opponent does get hit by either, then the very next set of non-projectile hitboxes Ness uses also cannot hit that opponent.(first hit of a multi-hit attack, such as forward aerial, will whiff that opponent, but the following hits can still connect)
How To Perform
Ness's up smash must first hit any opponent or damageable object while in its outreaching or spinning state. The outreaching state is typically used to hit, as its hitbox is stronger than the one in spinning state, and can knock the victim out of the way. If only outreaching state hits, then Ness has to charge his up smash for 6 - 11 frames after the hit. If the up smash is unstale, that equates to attack button being released between 24th to 29th frame of the up smash (including hitlag frames). If spinning state hits, the up smash has to be charged for 7 - 12 frames. The yo-yo can't hit anything after it is released into its swinging state.
This glitch works with down smash accordingly but requires that said down smash attack be canceled in its ending frames by an attack or effect (such as a Mushroom).
After using the yoyo glitch, certain other attacks can be used to replace the yo-yo hitbox with the hitbox of the attack used. The rules of the regular yo-yo glitch still apply when using a jacket.
Hitting something with the Yo-yo creates a special delayed hitbox refresh event. The purpose of the hitbox refresh is to allow a charged smash attack to hit a single target multiple times, while the Yo-yo is spinning on ground. However, the refresh event is missing an important detail that normal hitbox creation events always have: it doesn't setup Ness to have his hitboxes removed when his state changes. Thus, the refreshed Yo-yo hitbox can stay active after the smash attack has already ended.