It's kind of funny...I asked because I'm in the process of working on one.
I'll give the basic idea and the Specials for now.
Chibi-Robo could be a "
Turret-Fighter." In the games, Chibi-Robo has to plug into an outlet to recharge and gain energy. This would be more of a harmful thing in Smash, so to make him more true to his game mechanics, his
Down Special would be to plug his cord into the stage itself. While in this state, he has
limited movement options (only being able to go so far before the plug dislodges him from the stage), but his
attacks get much more powerful. Other than him removing himself from the "outlet," he
can be unplugged by a strong Smash attack. It is of note, though, that in this state,
Chibi-Robo has reduced knockback done to him. Certain melee attacks include the use of his plug, but these are mainly aerials, so Chibi
can't use Aerials while plugged in. Instead, he'd unplug himself.
His Neutral Special is the
Chibi-Blaster, which is really helpful when plugged in, as it's a projectile. It has slight homing qualities. Chibi's
Up Special is the Chibi-Copter, where he copters upwards with the propeller blades doing damage. Chibi-Robo's
Side Special is the Toothbrush. Chibi vigorously sweeps the ground in front of him with a toothbrush,
making that spot have less traction. If an opponent steps on that spot, they are far more likely to trip. As for a
Final Smash, calling in Giga Robo from the first game to smash the stage could be neat.
Just the basic idea for now.