Any4-7

This is the only stage in the game featuring upwind, which reduces gravity and allows you to float upwards by holding Marbles' glide.

Optimal

The fastest route through this level involves gliding between the gaps in the saws, which is a bit precise. Losing Marbles can be catastrophic if you don't know the backups.

Make sure to hold jump while gliding as it causes you to travel upwards slightly faster, saving around 1-3 seconds in the whole level.
Jumping off the platforms is slightly faster than gliding.
Marbles' hurtbox is positioned towards the back of the character sprite, which means you want to sort of "stick your face in the saws" rather than centering yourself. Experiment with it to understand the correct positioning. You can always stall to line yourself up if you don't get the correct position immediately.
After passing the second set of saws at 0:10.5 you can just drift right and continue gliding to the cannon at 0:19. This is only about 1 second slower as it skips the enemy bounces and platform jumps which each allow you to ascend faster.
Remember to hold jump when shooting out of autofire cannons to launch faster.
The final gap between the saw and cannon at 0:27.8 is a bit tight. If you take damage you can simply dropdash to the end. If you get sucked into the cannon, launching yourself into the rotating blades (taking damage) and dropdashing to the end is faster than going through all the cannons.
Landing on the final platform and roll-jumping to the goal is not faster than just gliding to the goal, as the upwind will cause you to jump too high and you'll have to fall back down.

If you make no mistakes and go for the fastest route, a time of 32 or better is good. If you play it a bit safer, a time of 36 or better is good. Beginners should aim for sub-40.

Backups

Learn these backups, as exiting the stage to recover Marbles loses a lot of time.

This video shows the backup routes after taking damage on the first or third row of saws.

This video shows the backup routes after taking damage on the second set of saws or getting pulled into the cannon at the end.