I posted a world 3 boss cling video a while ago but that was performed in the Heroes campaign. I tested that in the Normal campaign, and it still works. It works briefly as follows:

1. At the start of the level, dash to the side of the boss and attack.
2. You will regain your dash but the boss will probably move to the right after the slow-mo. Dash towards the right to try to cling to the boss.
3. Attack the boss (even if it does not deal damage) to regain your dash in case you fall off.
4. Stay in the top left corner of the boss and block the bomb. (The bomb is harmless.
5. The bomb should go down vertically, landing on the topmost platform. The bomb will kill the boss. As the bomb will also be able to hit you, jump away to the corners and levitate (jump in mid-air without directional input) just to be safe.
6. The bomb will deplete the whole bar of the boss, giving you the clear.

I recorded a low-4 section time for world 3 (in an All Worlds Solo run) after successfully pulling off this glitch. Here is the YouTube video for you guys.

Good luck!

A great discovery!