Last published challenges
Being Punished for Appreciating the Nintendo Switch Online Subscription Thingy
Bathaniel Nandy : Survive more than 1:00 without touching item boxes, without losing any balloons
With 8 participants, no teams

No Man's Snowman
Cool, Cool Glacier : Hit the Snowman on the Left (or Right depending on which way you look at it)

"Welcome to Mario Kart" or something along those lines
Cool, Cool Glacier : Complete the track with 64 participants

Beat the Staff Ghost
Dark, Dank Underground : Complete the track in less than 1:30 in Time Trial mode

The Monster
Dark, Dank Underground : Approach the Fire-Breathing Beast

Beat the Staff Ghost
Cool, Cool Glacier : Complete the track in less than 48s in Time Trial mode

Shy Pirates
Urchin Beach : Complete the track with Shy Guy

Driving a Boat
Urchin Beach : Get on top of the Boat's cabin.

I got a Funky feeling...
Fort Chasm : Finish in the 1st position in VS mode, with Funky-kong, in medium mode, without falling

Beat the Staff Ghost
Fort Chasm : Complete the track in less than 57s

^^'
Biome Bypass 1 : Complete the track in less than 2:46 in Time Trial mode, with Rosalina

Wasting time above a bottomless pit
Fort Chasm : Go to the sharp spot outside the fort that has no reason to be there

Beat the Staff Ghost
Stormy River : Complete the track in less than 1:04

Luigi's having a bad day
Stormy River : Complete the track in VS mode, with Luigi, in 22nd place

Waluigi's just showing off at this point
Stormy River : Finish in the 1st position in VS mode, without using any item, without making tricks, without drifting, with Waluigi
No teams

Battle against a machine
Stormy River : Finish in the 1st position in 1st place
In difficult mode, with 8 participants

Why is that indent even there
Stormy River : Go to the most useless part of the track (hint: it's on the rock side)

The Lonely Piranha Plant
Biome Bypass 1 : Visit his tiny Island :D

Orb of Power 4
Bathaniel Nandy : Hit 20 opponents with 12 participants
No teams

Time trial challenge
Complete the track in less than 2:35 in Time Trial mode
