Now that I think about it, why not make him like Pikachu? Starts out standing. But when running, he hops on all fours.
EDIT: Special Moveset!
Neutral Special: Car Crash
Frogger creates a car out of thin air, which speeds forward, this is one of Frogger's zoning options. In the air, it goes diagonally down. It moves about as fast as Luigi's Fire Ball, but has more cooldown. It does moderate damage.
Side Special: Alligator Ambush
Frogger creates an alligator, it moves back and forth in an area while chomping at the air. If it catches someone, they are held in place while taking minor damage. Allowing for a follow-up.
Up Special: Log...something. (Someone give me a better name please)
A water push lifts a log up, which int turn lifts Frogger up. The water has a pushbox.
Down Special: Firefly
Frogger places a Firefly onto an opponent. Or anywhere on the playing field. Frogger will then eat the firefly from any point in the stage. If an opponent is there, he will command grab that opponent (or if the Firefly is on the opponent obviously) If an opponent is not caught, Frogger will heal 2%