I found that Pichu idea. It wasn't Zap Cannon, it was Discharge

I still like it a lot.
It's hard to say which single character I would use. I sort of see him as a mix of the psychic characters (Ness, Lucas, Mewtwo). In the games, he rarely - if ever - uses physical attacks, so I imagine that he would be physically weak with more powerful magic. In Majora's Mask, he's always floating, so I imagine he'd be like Mewtwo in that his walking/running animations would have him hovering above the ground rather than actually touching it. He may or may not be hovering in his idle pose. I do think he could benefit from being a bit less floaty in the air than Mewtwo. Perhaps a bit faster and heavier, maybe somewhere between Ness and Lucas in speed and weight.
Thinking of his moves from the games, in OoT and TP, he mostly uses items and in MM, he uses magic. He has his blow darts from OoT, though I'm not sure if he can use them since he would be wearing the mask, unless he pushes it up out of his face before he uses it.
In TP, he has his instrument that summons those puppets, though I doubt that would be very feasible. He also has that torch / lantern of his. Perhaps he could use that in a couple of attacks and it could deal some fire damage. Maybe his Smash attacks could have his torch spit fire out of it? I could imagine his Down Smash being him slamming the torch into the ground and it spewing fire from both sides. He also has a teleport ability in TP, so that would be a good recovery.
Alternately, he could borrow Pit's original vBrawl recovery since he flies so much in MM. The Mask glows and gives him free flight for a limited time. He also has that scream of his. I could imagine that being a chargeable, radial attack (Like DK's Final Smash) that stuns anything in its range, with the range and volume of the scream growing the longer it's charged. Would that require an article? I'm not sure.
It's also possible that he could borrow abilities from the battle with Majora itself from the last battle. Perhaps his grab can be a tether using the tentacles from the Majora's Wrath portion. They could grow out of the Mask and grab things.
For his entrance, I would have him borrow his animation from Link or Pit, where he comes down in a beam of light. I would change it so that he's limp and hanging from the Mask, though, then comes to life as he touches the ground.
What do you think? Does any of this sound about right, or did I just completely miss the mark?
EDIT: Say, are models used in entrance animations (like Mario's Warp Pipe) articles?