I think some have discussed Pichu before, and I know most people hate him, but I thought of an idea that could make him work to a degree.
For starters, Pichu is still frail as ****. No way around that. However, Pichu is nimble as a flea. He has insane mobility, with great recovery, great jump height, good air speed, fast dashes, fast falls, the works, to compensate. Pichu's attacks are powered by electricity, making them do large amounts of damage with moderate knockback. However, Pichu does damage himself in the process. As such, Pichu becomes the ultimate high risk high reward character, complete with great mobility and combos and power, but a defense game that is absulutlty pitiful.
I guarantee others must have suggested something similar before, but this is how I would have Pichu reworked into Project M. Also, would be cool to have the last Melee character come back...
Also I support Sami, Isaac, Andy, Ridley, Black Shadow/Ganondorf, Ray, K Rool, Bowser Jr, and Dixie Kong.