Here is the full list of all 21 Slip achievements.
Earn 25% star completion.
Beat any level without dying.
Earn a score of 100,000 or more in a single level.
Collect 100 powercubes in a single level.
Earn a speed bonus in any level.
Turn off your toaster.
Beat the first boss.
Beat the second boss.
Beat the third boss.
Earn a score of 200,000 or more in a single level.
Earn a score of 300,000 or more in a single level.
Earn a score of 400,000 or more in a single level.
Beat any level without dying and collecting all powercubes.
Earn 50% star completion.
Earn 75% star completion.
Earn 100% star completion.
Enter 2 Hypercubes in a single level.
Hit 9 checkpoints in a row without dying.
Clear all the challenge levels on any difficulty.
Collect 10000 Powercubes.
Beat the final level with the "Steve's Bane" unlock equipped.