Challenges list of LuigiDawg
It's Time!
Big Ben : Survive more than 1:30

Tiem
Big Ben : Eliminate 1 opponent by yourself

Time Trials
Big Ben : Finish the game in the 1st position

Time out!
Big Ben : Hit 3 opponents

'tis Big
Big Ben : Test the Arena!

M.P.I.Q.
Waluigi's Island : Survive more than 1:23

Zzzzz...
Dark Mode Circuit : Finish 1st 2 times in a row

Dihckourd
Dark Mode Circuit : Finish in the 1st position with Dry Bones, with 100 participants

Better at Night
Dark Mode Circuit : Complete the track by starting with 20s delay

Why is Light Mode even an option?
Dark Mode Circuit : Test the Track!

Much Better.
Dark Mode Circuit : Finish in the 1st position
In difficult mode

GO BACC
Light Mode Circuit : Go behind you to around the puddles' area in less than 2s

SPEED
Light Mode Circuit : Finish in the 1st position in VS mode, in medium mode, with 12 participants, without making tricks

MY EYES
Light Mode Circuit : Complete the track with King Boo

I can't think of a good challenge name.
Retro Desert : Complete the track with 2 participants

retrosimulator.exe has stopped working
Retro Desert : Go south.

LEVEL COMPLETE
Retro Desert : Complete the track

2000 POINTS
Retro Desert : Finish 1st 2 times in a row

Smol Godzilla
Rooftop Speedway : Finish in the 1st position with Bowser

That's not Chocolate, Jimmy, don't eat it
Greatest Achievement Stadium : Break the Box in the mud.
