I found this on USBGecko forums, but in the ocarina section. =D
Moveset swapping is good for the looks,but when you want to play with an move swapped character...expect your game to freeze up at some point.Off course,there are some characters at NEVER freeze,but they lock themselves in their default "T" pose and are unable to move.
Also,liero116 at GhostNeo said this:
"See the way this works is that when replacing move sets, the characters MotionEtc (animations and other junk file) can only be replaced by others of equal or less file size. For instance, Dedede has the largest MotionEtc file size, so he can use anyone’s moves. ROB, on the other hand, has one of the smallest file sizes and the only two he can imitate are Pokemon Trainer (guaranteed instant freeze) and Giga Bowser (highly likely to freeze)."
Also,if you change the moveset of say,Ness,just trying to spawn his Yoyos will cause an freeze.Best to do is play while the TV is muted,so you don't have too much problem with the "BRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR" freezing noise.
See,here is also an list I made.This list goes from lowest filesize to biggest filesize (from up to down):
Pokemon Trainer -lowest filesize-
ROB
Game & Watch
Ice Climbers
Link
Ivysaur
Kirby
Jigglypuff
Zero Suit Samus
Olimar
Ike
Charizard
Luigi
Yoshi
Samus
Sheik
Falco
Marth
Meta Knight
Mario
Squirtle
Donkey Kong
Bowser
Lucario
Lucas
Pit
Ness
Fox
Toon Link
Wolf
Diddy Kong
Captain Falcon
Ganondorf
Pikachu
Sonic
Zelda
Snake
Wario
Peach
Dedede -biggest filesize-
Example: Link can only swap moveset with whoever is over him,because they are of an lowest filesize.