So, since AniMewtwo has been represented by the armor, why not Mangewtwo (I try hard, okay)?
Mostly I'm talking having a spoon strapped to its back, but if that doesn't make it distinctive enough, it could have the dark purple and white color scheme of early artwork (as opposed to the normal costume's pink and off-white) or be black and white (mimicking how the manga's actually printed), and the gauze Blaine had on his arm because of their connection.
I think an N64 could work as a ROB head, but more amusingly, hands based off the controller. It could use that awesome Atomic Purple everything came in back then, and the Gyro could be colored like the logo.
I played through Chibi-Robo! recently, and I think a ROB based on the eponymous robot would be cool. Their heads, arms, and pillar-body are nicely analogous, and ROB's cord could have a plug at one end, plugged into himself. ROB's base, torso, and gyros could have designs based on th Chibi-House, Chibi-Doors, Chibi-Helpers, and Telly. There could also be another costume for Giga Robo.
Another major character in the game is the manly, dramatic, heroic, futuristic, bird-themed bounty hunter,
Space Hunter Drake Redcrest!!
He yells at you (usually his own name)
every time you talk to him (it's actually his first rule of Justice), accompanied by an explosion of orange smoke and confetti behind him. As special GFX, the explosion could appear during the costume's entrance, taunts, win animations, secret taunt, and Up-B's explosion. There's also the notion of having the SFX that goes with it, and even making that pose one of the costume's win animations, if anyone really wants to put that much time into a relatively obscure costume. Partway through the game, he learns a super attack that hits an opponent with a giant chunk of ice, so that could be implemented by making the (if you haven't figured out yet who I'm suggeting you put Redcrest's outfit on) Falcon Punch icy and replacing the actual falcon with ice, but that may be going a bit overboard.
Dark Suit and Light Suit Samus could swap the fire/ice effects with light/dark effects, since that's basically what those beams were in Echoes.