According to Nintendo, Mario transforms into his outfits, he doesn't wear them.
While playing New Super Mario Bros. U at a recent press event, I came across an interesting revelation. I asked the Nintendo representative which level had the Flying Squirrel suit. She answered, and then corrected me, saying that Mario transforms into a Flying Squirrel. He doesn't wear a Flying Squirrel suit.
For years, I referred to various Mario power-ups as Tanooki Suit, Frog Suit, etc. Was this truly always the case? I asked the rep if this had to do with PETA. "No," she said. "It's always been that way." And then she highlighted the fact how fans have run with the suit terminology.
Naturally, I went and checked to see if Nintendo mentioned suits in any of their previous games (thanks Mushroom Kingdom). Super Mario Bros. 3, which introduced the concept, refers to the Frog Suit and Tanooki Suit in the manual. However, they both say that "Mario changes into [the suit]." Super Mario Bros. 3 on the Wii Virtual Console and Super Mario Advance 4 still refer to the "transformations" as Frog Suit, Tanooki Suit, and Hammer Suit.
Super Mario Bros. 3 seems to be the worst offender of the suit references, as the Nintendo Power strategy guide refers to suits all over the places, but with more detail than the manuals. There's the P-Wing ("A high-powered Raccoon Suit, it lets Mario fly at will for an entire stage, or until he gets hit."), the Frog Suit ("Get ready for aquatic action with the Frog Suit. It lets Mario swim like a frog and leap like one, too."), the Tanooki Suit ("This fuzzy brown suit gives Mario all the powers of Racoon Mario plus the ability to turn into Statue Mario!"), and the Hammer Suit ("The Hammer Bros. Suit is a crafty outfit; the Hammers he throws are powerful, and the shell is fireproof!").
Here's a quick list of how other games refer to the suits/transformations:
- Koopa Shell (New Super Mario Bros.)
- Propeller Mushroom (New Super Mario Bros. Wii)
- Penguin Suit (New Super Mario Bros. Wii) - "Strap on the Penguin Suit..." (from the official website), referred to as the Penguin Suit in manuals and marketing
- Bee Mushroom (Super Mario Galaxy)
- Boo Mushroom (Super Mario Galaxy) - "He'll morph into Boo Mario." (from the official website)
- Cloud Flower (Super Mario Galaxy 2) - "He'll become Cloud Mario." (from the official website)
- Rock Mushroom (Super Mario Galaxy 2) - "...become Rock Mario." (from the official website)
- Boomerang Flower (Super Mario 3D Land) - "[the power-up] turns Mario into a Boomerang Mario" (from the official website)
- Super Leaf (Super Mario 3D Land) - "Grab a Super Leaf and suit up as Tanooki Mario" (from the official website)
- Flying Squirrel Mario (New Super Mario Bros. U) - "...transforms into Flying Squirrel Mario" (from the E3 2012 fact sheet)
So it seems like Nintendo's company line isn't entirely accurate, as back in the '90s, suits were a common reference point for a variety of power-ups. Lately, they seem to be eschewing that, though the Penguin Suit lingers as one big, glaring hole in their plan. Outside of that and one token line of copy referring to Mario suiting up, it seems like all he does is transform these days.
Looking at recent press releases from Nintendo of America and Nintendo of Europe, they don't seem to both corroborate the transformation angle. Nintendo of America's Super Mario 3D Land press releases refer to changing into Tanooki Mario, while Nintendo of Europe talks of the Tanooki Suit.
Super Mario Bros. 3 seems to be the one game where suits were a focus. Even in recent interviews, Hammer Mario, which was in Super Mario Bros. 3, still has to get a Hammer Suit to transform. Still, there is tiptoeing around saying the Tanooki Suit, as that same interview purposefully never refers to a Tanooki Suit.
However, Mario Tennis Open has several unlockable costumes that look like they very well could be suits. So, to summarize, I guess Miis can wear suits, and Mario can only transform in Nintendo's eyes.