Ninten is the hero of the original Earthbound. He's an obvious, yet not so obvious choice. He could easily be a clone of Ness and Lucas (despite him being the first of the three). However, he could have a unique moveset that would be a great addition to Smash Bros.
The only move I think he should have be similar to Ness and Lucas would be his bat. However, it would be much stronger and slower than Ness's and could even break through shields and send explosives back.
He has many items such as an ocarina, slingshot and a boomerang.
Ninten has several other forms of PSI that Lucas and Ness have yet to use yet. There's darkness, hypnosis, paralysis, and more. I think his PK Beam could be his standard special attack. It could be a charge move, but it would be horizontal rather than a vertical attack like PK Flash or PK Freeze. His Quick Up could be somewhat similar to Fox's side b move, but he could control how far he goes. His recovery move could be his ability to teleport.
Maybe one of his abilities or at least taunts could use telepathy. It'd be fun as an easter egg to see what other characters are "thinking"