Chain Jacket glitch
The Chain Jacket glitch is a glitch in Super Smash Bros. Brawl that causes Sheik's Chain to use the hitboxes of the last attack Sheik used instead of its own. To perform the glitch, the player must short hop and, at the highest part of the jump, use the chain. (It can be done without a short hop, but it is the easiest way, as the timing is dependent on how fast Sheik is falling.) This glitch is very similar to Ness' Yo-yo Glitch in Super Smash Bros. Melee.
The four hitboxes of the chain will each take on the properties of the corresponding hitbox from the last attack used; for example, the first hitbox of the chain will act like the first hitbox of the previous attack. Attacks with a sweetspot or sourspot will therefore cause the chain to have a sweetspot or soutspot, though depending on the move the hitboxes may be in a different order (it may be on the grip instead of the tip, for example).
If the glitch occurs without Sheik having used an attack yet, the game will freeze.
The hitboxes of Sheik's chain in Brawl behave differently than other hitboxes - they are not physically attached to the chain when they are produced, but nevertheless move around with it. This unique programming is achieved by referring to the data of the current hitboxes and relocating them as the chain moves around.
The glitch is caused by the hitboxes on the chain not being produced if Sheik lands during a specific frame of the starting animation. Since the chain's hitboxes aren't produced, the game is forced to use whatever hitboxes are left over from the previous attack. If no attack has been used yet, then no hitboxes are there to be used, so the game crashes.