Noclip bugs are where the player is able to go through blocks, usually by unloading the blocks and then reloading them after falling through, due to the fact that offscreen blocks are unloaded and you can walk or fall through them.
Causes[]
The main way to cause a noclip bug is to resize the window to hide certain blocks, and then put it back to normal after passing through.
The game's collision code used to use "getElementFromPoint," which gets an element from a point on the screen. When blocks are off-screen, they are not in the screen, therefore, the game couldn't detect them.
You may also cause the bug from a camera launch.
Camera launch bug[]
Camera launch bugs are where the camera can be moved in a direction without affecting the player, allowing them to noclip through unloaded blocks.
Vertical[]
Signs used to be able to cause a vertical camera launch bug, but this is no longer possible. You are now only able to do horizontal camera launch bugs using sign dialog.
a vertical camera launch as a solution to the level Dumbcar ladder, though the level had no name at the time this GIF was taken, 12/24/2020.
Horizontal[]
even though a vertical launch using the uppermost sign was the intended solution for Dumbcar ladder, a horizontal launch also works.
Horizontal camera launches are still possible, and can be used to go through floors and walls, by moving the camera to a position where it barely includes the character, and no blocks left of it, rendering the blocks no-collide.
Clipping through horizontal walls in the rewrite of the game is still very possible. If you run towards a wall at the right position, there is a chance that you will pass through the wall! Although this can be used to clip through walls, you also travel downwards at an incredible speed.
Another way to clip through walls in the rewrite is to fall through the very edge of the wall. If you do it correctly, you will appear to slide down the wall in the wrong direction. Jumping while in this state will push you into the wall enough to not be pushed back out, and you will go through. The downwards speed still gets applied, unfortunately.
horizontal launch bug on level Goldfish