Desynching is a technique exclusive to the Ice Climbers in Super Smash Bros. Melee, Super Smash Bros Brawl, and Super Smash Bros Ultimate. It involves purposely lagging one of the two characters to time their attacks separately.
The easiest way to start desynching is by doing an attack at the time the Ice Climber the player controls (usually Popo) can't attack, while the other can. Example, by doing an attack (with a certain timing) after a spot dodge, only Nana will do the attack. The timing can be practiced by taunting after a spot dodge; if only one Ice Climber taunts, desynching has been achieved.
Double Vision: An Ice Climbers Guide to Desynching is an instructional video presented by Nealdt which teaches and demonstrates the many uses and techniques of the Ice Climbers' extraordinary desynching technique. The video is meant to be used hand-in-hand with the provided thread on Smash World Forums. This thread contains detailed descriptions on how to perform the various techniques, and advice on how to implement them into your game. It is suggested that the text be read before the video is viewed.