The robots are built up with 5 parts:
Body: The chest, arms and head.
Legs: Legs and feet.
Gun: Right hand weapon, usually a gun but can be other stuff like drills.
Bomb: Left hand weapon, usually a cannon that fires bombs.
Pod: Jet-pack-like thing that fires small bombs or mines.
So you could assign:
Standard Smash: Change Gun
Down Smash: Change Leg power-ups
Side Smash: Change Bomb weapon
Up Smash: Change Pod
And use the usual attacks to fire whatever weapon he has armed.
And assume the bodywill ave maximum armour on at all times... and could get progressively shot off as the game wears on?
I always like characters that give an extra dimension to tactics.