I think it could be kinda like toro in playstation all stars, or pokemon trainer, or Zelda and sheik pre-sm4sh, where a certain attack could change disguise, like use nair for sparky, fair for genius, dair for dragon, bair for cosmic, uair for wicked, captain in water, and goes back to thief with a taunt, like kirby does, and add some WMOD music, like the Poobah/Ka-Bloom/Lavachomper/Stuffy battle theme, or Cannoli's battle theme, I think his Final smash could use all of the disguises, shoulder bash, zap them, draw a block on their head, shock them, missile them, burn them, shock them, punch them, and pick them up and drop them.
You that would be really interesting. Much more intersting that what I was thinking of: Basically his moves just all transform him on the spot. (but after the move he would poof back into theif wario instantly)
Your mechanic sounds AMAZING.
In theif wario form he could be more nimble than others but since he cannonically has NO attacks all of his moves would just have to be what he transforms into's moveset so it would still have that transform on the spot thing I'm thinking of where the animation happens very fast. Maybe its also covered up by the puff of smoke seen in the game.
Sparky could be like pikachu/wario with ness's Bup, pika Bdwn, shoot a wolfe gun when side b, charge up to shoot the three bolts like in the game with regular b, if in air b shoots a bolt below and side be shoots it diagonally down.
Genius: fights with nonlethal gag/slapstick weapons but with a technological twist in his A set and are fast execution: boxing glove extender, mechanical giant mallet that folds out from nothing but also looks plush, fake gun that hits the person with the click flag, weighted tailcoat (bair), and other weapons I boosted from the joker. B moves would have to do with invisibility (maybe even making weapons invisible) or stunning the opponent at risk of long charge rate, with a helicopter hat for Bup.
Wicked: Since wicked wario cannonically doesn't fight at all he could just be a floaty wario with wario land moveset except maybe all his B moves are wing based (metaknight B moveset)
Captain: Has a sub he can pull out with B but has the same A moves as the wario land moveset outside the sub.
Dragon: Bowser/k-rool hybrid moveset
Cosmic: A tank version of fox/falco/wolf, B down charges a thruster that looks like wario is farting and exhausts hitting on either side. Bup is jet pack.
Arty: Sits still/paints and things around him happen carrying a stool, paintbrush, and canvas if hit into the air. A moveset involves smashing a canvas, or stool into people or splashing them at short range with paint that does burn damage, or freezes, or electricutes. Bup warp door is created beneath wario and he warps upward and after a time the doors both fall, can be used as platform by others or can fall on them doing damage. Bdwn, side, and b all paint something after different lengths of charge but if it isn't charged enough it still paints a poorly drawn poo on the enemy that can damage them to different effects. (lol)
I WOULDNT CHANGE THAT FINAL SMASH AT ALL SOUNDS DANK LMAO.