This is my proposal for character customization.
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Stickers and Trophies can be used to create moves for your character.
You can select a character and a specific move you choose will be put on your character, and you can keep "stealing" moves. However this already sounds broken, and thus, the moves will be a huge nerfed move. You can enhance their stats using stickers and trophies which enhances a specific type of move.
Let's say you steal Mario's forward tilt and that does 10%. Your stolen forward tilt will do 4%. Use must use a foot sticker to enhance its power.
However, each sticker has different effects and power increase. You could have a foot sticker that has "40% chance to increase a foot-type move by 3% damage with flame effects", or "10% chance to increase a foot-type move by 5% damage with darkness effects".
This will make it a unique way and automatically make stickers/trophies a useful item to collect while completing random parts of the game. And if each sticker/trophy has different chances, types, effects and maybe even rare enhancements ('pierce through an opponent's move with a 10% chance', etc.) that will solve the broken issue.
There would eventually be a limit on how much you can enhance a move. If Mario's forward tilt does 10% damage at default and not stale, your move cannot surpass that. On the other hand, if Mario's stolen forward tilt can only be enhanced 3 times, you cannot increase that unless you use a trophy or Golden Hammer or something. If a sticker fails the enhancement will decrease to 2 even though it did not work.
A character's design will probably be a Mii but you can steal textures and stuff from other characters as well, or design your own by drawing on the Wii U GamePad or Nintendo 3DS. The weight and height of your character can be no bigger than the character with the most weight/height, such as Bowser. You cannot be heavier nor higher than Bowser.
You can also do this with hitboxes. If Mario's forward tilt reaches starts at his thigh and extends to his foot, you cannot move a hitbox 1.3x farther than his boot or his thigh, and since the hitbox is attached to his foot, you can only move the hitbox along his foot, so you can't make his move hit behind him when the animation shows it doesn't.
Voices and taunts can be implemented with your own voice or stolen sound effects from other characters. The microphone on the 3DS or GamePad can record your voice, create a file, and then you can apply that sound effect to a move, a taunt, or whatever.
You can save characters and share them. You can create up to 3 custom characters.
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So that's what I think could happen in the most logical way, not in the way I want. I don't mind how Sakurai does it because I probably won't make my own character anyways.
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