There are multiple spots in this game where you can clip in the wall and do an extra jump. It's hard to practice, but defenitly possible.

The main usage for this is on the last stage. You can skip the surfing minigame. Collect all keys of the bottom (from right screen you just need 1 key) and then go to the door behind the scuttle which jumps. You can jump a few pixels in this wall, and as result you get pushed out while landing. But in the moment you get pushed out, you can fire a jump again. It's a nearly frame perfect press, but luckily you have a frame for each pixel you get pushed out. If you clip for 5 pixels in the wall, you can 5 frames where you can do a jump again. For this one, you have to do 3 jumps in a row. 2 jumps on the platform, the you can rest as long as you want, and then do a last one on the next platform. From here you can collect keys until you have 27, do the game for the umberella and jump with them to the end skip.