Shin Megami Tensei's Jack Frost:

http://i.imgur.com/YOnf6Go.png

Okay, hear me out:

1. We know Smash Bros will use non-Nintendo characters. Proof:Snake & Sonic.

2. Smash has used Fire Emblem characters for two generations now.

3. There is a Fire Emblem x Shin Megami Tensei crossover announced for wii U.

4. Shin Megami Tensei 4 is going to be a 3DS exclusive (at least it looks like this so far).

5. Jack Frost is the series mascot.

6. He'd be very easy to add. They already have a freeze effect. They could just re-texture Charizards breath attack and add the effect instead of damage. He could easily replace the ice-climbers and have similar controls/movement. Maybe be heavier with a weak jump for his size, considering his movement patterns in SMT indicate he's not very mobile despite his size. And His smash could just be turning into Black Frost, kind of like wario's.

It would just be a perfect addition to boost interest in the SMT series, the same way a ton of people only discovered mother and FE after Melee was released.

Atlus would benefit from the exposure, and Nintendo would actually have some stable third party support from a company that can make they type of games a lot of us felt they gave up on with the Wii.