Your headcanons

Super Mario Maker is canon and everyone who owns the game exists as a god in the Mario universe who each rules over a domain that they created. The nature of these domains depends on the god who rules over it.
 
So Mario Sports Superstars shows Metal Mario taking off his cap.

Since the Metal Cap is supposed to be the item that makes Mario metal, he wouldn't be able to take it off without reverting back to normal. This proves my head canon that Metal Mario is actually a robot true.

Why a robot would have a detachable hat, I'm still trying to work out.
 
My headcanon is that Baby Luigi is not great at sports, mostly because it's pretty much his first time playing and he's rather uncoordinated, at least, compared to Baby Mario.
 
Peach has great physical strength, seeing how effortlessly she can swing a frying pan with one hand in SSB4 and carry a Brolder in 3D World. Her strength doesn't match that of Mario and Luigi however.

Peach and Zelda are great friends, judging by their interactions in the SSE.
 
Is that really just a headcanon, though? It's pretty much all but directly confirmed in-game. In the beginning cutscene for Super Smash Bros., Master Hand does the "3, 2, 1" just like the announcer does before a fight.
 
Bump.

Only characters with caps get Metal Caps out of Metal Boxes. Other characters get other articles of clothing. Peach would get a Metal Crown, Yoshi a Metal Saddle, Bowser a Metal Shell, etc. I'd get Metal Glasses.