I think this would be amazing if the Mii was a playable character. If I were to put the Mii into the game I would make the character creation similar to the modern WWE games. This is how I would work things out.
1.) Choose Mii:
Pick a Mii from your collection to start creating your character. Remember, your Mii character’s gender determines the gender of your character.
2.) Select Body Type:
You can choose from 3 classes: Lightweight, Middleweight, and Heavyweight. Maybe you could even unlock some weight classes later on with the tokens earned throughout the game [i.e. Featherweight and Super-Heavyweight]. Weight class affects your characters overall make up [Speed, Weight, Strength, Agility, etc]. Let’s give out examples for the 3 weight classes.
Lightweight characters [i.e. Fox] are very fast and agile and strong to an extent. However, they don’t weight much and get tossed around more easily than other characters. Heavyweight characters [i.e. Bowser] are somewhat sluggish and laggard. However they make up for that with awesome strength. Also their weight acts like an anchor and makes the character hard to throw around.
Middleweight characters [i.e. Mario] are well balanced in everyway. Not too strong, not too slow, etc. You get the picture.
Once you’ve picked the weight class you’re most comfortable with, we could move on to the next step.
3.) Select Height:
You can change your characters height from 3 selections: Short, Average, and Tall. This should affect your character is a way. My idea of this is that the shorter the character is, the slower. And if you’re tall, you run faster.
However, if you’re short, you could be more agile, while if you’re taller, you could be unnoticeably laggard [and an easy target due to size]. Average height is proportionally balanced.
4.) Select Body Shape:
Just for fun. You could be Skinny, Slim, or Fat.
5.) Select Attire:
Choose what your character wears. Give him/her a hat, a moustache, a dress, a pair of boxing gloves, EVERYTHING. I think this would be a neat feature. And maybe this could be done with the other standard SSBB characters as well [I doubt it]. I also suggest some clothes to be unlockable and only to be purchased with Smash Tokens.
6.) Pick a Final Smash:
I think there should be multiple Final Smashes to choose from. One of them should be the giant hand from the Mii Application picking up one or two of your opponents and throwing them off stage.[courtesy to samXcor3]. And there should be some uber-finals that should be unlocked through Smash Tokens.
7.) Give Your Character a Name:
You get the idea.
8.) Test Run Your Character:
If you aren't sure about how he/she attacks, moves around, or uses his/her final, test it out. Once done testing, either go back and edit your character or click save.
CONGRATS YOU JUST MADE YOUR CUSTOM Mii CHARACTER!!
I think there should be like a limit of 20 created Miis. And how to select your mii? When going to the character select, click the character Mii. Then a box will pop up showing all the customized Mii's you can play as. Pick one of them and get ready to brawl!
So guys and girls, whatcha think?
And don't be shy to post your ideas as well. THIS I think is an idea Nintendo should consider giving a try.