Here is the full list of all 26 Nickelodeon Kart Racers 3: Slime Speedway achievements.
Buy everything in the shop
Get 150 Victory Points competing in Online Matchmaking
Play 20 local multiplayer races
Finish a cup in first place 40 times
Perform 250 Slime stunts using wave edges
Hit opponents 500 times with items
Get a blue-spark drift boost 21 times in cups
Win 10 arena matches in any mode
Beat all 36 Ghosts in Time trial
Get 100 Victory Points competing in Online Matchmaking
Play online with at least 3 other players
Complete 50 Double Dares
Play an online race with a friend
Complete all challenges
Unlock 15 crew members
Get 50 Victory Points competing in Online Matchmaking
Drive through a Kart Wash 30 times
Beat 8 Ghosts in Time trial
Buy 5 different things in the shop
Complete your first cup
Finish a cup in first place
Achieve the "Slime legend" score in Slime sliding 20 times
Unlock 5 chiefs
Perform 250 Slime stunts
Drive through 50 boost pads
Complete a race without getting hit once