A moveset swap is a hack which causes a character to take on the animations and moveset of another character. This is doable in Super Smash Bros. Melee, Super Smash Bros. Brawl and Super Smash Bros. for Wii U, though all require the use of hacks in order to be accessed.
The exact results of moveset swapping can vary; while some characters can impersonate others with relatively little trouble (most commonly clones or semi-clones, such as Fox and Falco), a majority of combinations are extremely unstable, often crashing the game whenever an attack is inputted, or even by merely attempting to load the character.
In Melee, move-swapped characters retain their body proportions and simply rotate their bones to match the new animations; for example, Donkey Kong's legs would pass through platforms if he was given the moveset of someone like Jigglypuff. However, in Brawl and after, characters change body shape to match their new animations, leading to unique distortions; for example, a character with short legs such as Mario would have his limbs stretched if given the moveset of a tall character such as Captain Falcon.
If the character used has loose hair, a dress, or the like, it will remain stiff if the animations do not include it. This extends to all parts of a character; for example, Mario's ring fingers will remain "closed" when using Yoshi's three-fingered animations.
When a moveswap is used, most standard moves retain their characteristics from their original character. For example, Yoshi can use Luigi's forward smash without difficulty. However, more complicated moves may result in a "hybrid" move, such as using a stall-then-fall when the original character does not have one. Special moves in particular have unpredictable effects, ranging from a surprisingly glitchless combination to a character-freezing situation - such as Mario using Skull Bash (flying sideways at a constant speed until he gets past a blast line) and Falco using Dancing Blade or Dolphin Slash (freezes in place while falling after the initial animation).
As hitboxes are attached to bones based on their ID number, and characters have different numbers of bones, moveset swaps may result in hitboxes being placed in unexpected locations.
As a meme
While not as widespread as the Wombo Combo, videos demonstrating moveset swaps became a minor internet phenomenon in the years following Brawl's release, particularly due to the heavy interest the game attained. The popularity of the videos can be attributed to the unusual, distorted appearances of most of the characters, due to the limbs and bodies of characters being contorted as to fit the models of other characters. Amongst players of the games, the unusual effects of the various attacks can also be of various interest.
Of all the moveset swaps featured on video sharing sites like YouTube, the application of Ganondorf's moves to Pikachu quickly became the most popular. Pikaman (sometimes referred to Pikadorf, Freakachu, Longchu, and other such nicknames) attained this popularity primarily because of the distortion of the famous character of Pikachu; in addition to standing on two legs, the long, gaunt appearance of its limbs stand in stark contrast to its large body and ordinarily stubby limbs.
In addition to its infamy as a meme, Pikaman has attained a large fanbase amongst the community. In addition to in-jokes about Pikaman's supposedly powerful fighting prowess, videos have also been made featuring the character in actual brawls, and file replacement hacks have also been created as to allow the character to be playable without the need for setting up a moveset hack.