I beat all these challenges (mainly set by Gamefaqs and I just tried them anyway)

[cheat-master30]

I beat Mecha Bowser without the spring mushroom
Got the Sea Slide Silver Stars without the Bee Suit
Bubble Blastoff star in Deep Dark Galaxy without the Ice Flower
Ghost Ship star in Deep Dark Galaxy without the Fire Flower
Boo in a Box without rotating the box
Still need to try some more challenges...

[GenericMan121]

I'll try and think of some...

[cheat-master30]

Yeah, I need some good challenges.

[blubomber17]

CAN YOU...

Beat Luigi's Purple Coins in under 2:00?

[cheat-master30]

Need to try that. Not sure whether it will be hugely difficult, and I'd be more likely to fall than run out of time...

[blubomber17]

Um... maybe 1:30? Or is that starting to border impossible?

[cheat-master30]

I have no idea.