R.O.B the Robot
There are two games that used the ROB accessory. Gyromite and Stack-up. I've never played Stack-up, but Gyromite might be a good place to draw moves from.
Perhaps the character would work like this:
You would control Professor Hector (R.O.B's "Creator" in Gyromite and Stack-up, as seen in the loading screens for Tetris DS) and he would punch and kick and all that stuff, but he would have no B-moves of his own. all of his B moves would be to send commands to the ROB that follows him Ice Climbers style (In a curious switch from Gyromite, where you play as ROB, and Hector is the uncontrollable one), except possibly his UpB, which would be independant from ROB (So as to have a useful recovery move.).
Perhaps Rob would shadow you like Nana and hit enemies along with you, or perhaps he would just follow you around (and not be able to be hit).
Or perhaps, ROB is the controlled one, but he is shadowed by Professor Hector, who is presumably controlling Rob. The catch? ROB cannot be KO'd himself, but the good professor can. Rob is basically one big disjointed hitbox that can be knocked about, and if Hector is KO'd you lose the stock, so it would be a double game of protecting the prof and KOing the enemy. Hector should be very light and fastfalling, just for balance sake, so even if you go up against a very good ROB, Hector can be knocked clean away with a few good hits. Would that be Broken, or just the opposite? I don't care, It sounds awesome is what it sounds like.