A Hard To execute glitch, but saves Considerable amounts of time when used right.
Press P for shop at the beginning of the game.
Select Rainbow Trail
Staying still with this, can trigger a jump.
Jumping specifically, then staying still can teleport you to the top of the screen, and travel vertically through Walls.
Also, I know when nobody can get a deathless, much less an optimal run, this is not very
useful, I am just sharing it anyways.
Technical Reason.
Since the rainbow trail is RAINBOW, the colors could affect you if they were the
correct colors in the code.... but they're not the right colors so why am I talking about them? Well, as the trail slowly fades, it is considered a different color to scratch. This sometimes causes some colors to affect you while your player is still.
pink makes you jump. helpful, but not too useful.
Purple, on the other hand, a mechanic learned at the end of the game, teleports you to the top of the screen. This is VERY useful. You can straight-up skip some levels.
I did not explore this to its FULL extent, so there could be more effects with this Glitch.
Example: