Mario's next animal power-up suit.

[Xiahou Ba]

Make Mario wear a human suit

 

[Dr. Peach]

How about turn Mario into a wolf like Alucard does in Castlevania: SOTN?

 

[Xiahou Dun]

And then a sassy imp-like princess of the period between late afternoon and evening comes in.

 

[yoshiking14x]

Caterpillar Mario: He uses a flower that resembles the flower of a Wiggler and he receives a costume that resembles a peanut and his shoes have suction cups and he can walk in walls and the ceiling too.

 

[Dr. Peach]

Who doesn't like Mario, Luigi, Toad and Peach turning into a Wolf like Alucard does in Castlevania: Symphony of the Night? I would totally enjoy it.

 

[Noct]

Ape Suit Mario... no wait.

Mario Kong.

 

[Pinkie]

Ape Suit Mario... no wait.

Mario Kong.

Nooooooooo-*shot*

I still want Gator Mario.

 

[Starlight24]

Zero suit Mario

 

[Mister Wu]

Zero suit Mario

That was actually already done in official material, at least three times, one even in-game:

Spoiler

 

[TinTinfinite]

Magikarp Mario

(B) to splash

 

[Mcmadness]

Luigi suit Mario

 

[Hobbes]

birthday suit Mario