I found this glitch with @TylerCSpeedruns

To perform this glitch, climb up the ladder next to Level 1. There will be a specific corner where you need to clip. This is how you do it.

In first person/shift lock, angle yourself to the edge of the corner. Get the camera out of first person/shift lock, and then make it touch the wall. Zoom into first person/shift lock while it is touching the wall at the same time and it can teleport you to the top of the platform.

Success Rate with First Person: ~10% Success Rate with Shift Lock: ~60%

After this, walk to this exact location and complete this stage. This should let you skip all the way to stage 24. Complete the rest of the game WITHOUT DYING (this is required as the game does not save your checkpoints after doing the clip). Now you’ve completed Super Platformer Classic with a corner clip skip!