I was looking over my other post, and I realized I could probably have formatted my Ninten +1 reasoning more like the ones in the OP, so I decided to go on ahead and do that.
Ninten (Mother / EarthBound Zero)
Background/Reasons: The only main Mother character still not playable, and the star of the first game. Not a walking spoiler. To prevent him looking too similarly to Ness, he can wear his clothes from the live commercial rather than his official art.
Moveset: Quick Up (temporary speed increase), Power Shield (which blocks physical rather than energy attacks), PSI Hypnosis (like Jigglypuff's Sing), 4th-D Slip (Teleports), and PK Beam (Unique to Earthbound Zero) are ideal techniques, though he also has a boomerang and a slingshot.
As a Final Smash, he could have either PK Beam or a combination of PSI Life Up and a number of Shields that would heal him completely and give him temporary invulnerability. Maybe add some buffs like Offense Up and Quick Up to make him faster and stronger during this period a la Wario Man. Finally, he could have Brain Cyclone as a Final Smash, which would work in three waves radiating from him. The first would spike characters it hits down, the second would stun them, and the third would have large knockback.