Any3-B

There are a number of ways to completely skip this boss, completing the level in 5-8 seconds.

Optimal

Begin by switching to Checkers and dropdashing across the platform. Do a quad jump across the gap, swapping back to Marbles and shell jumping up to reach the goal. Since Marbles is needed for Spicy Ice Speedway, and this is the fastest individual level strat anyways, this strat is optimal. Be careful not to shell jump too early or you will collide with the ceiling and not have enough height to reach the goal platform.

Early bubble/Easier quad jump

If you took damage at the end of End of the Raybow and reach this level with solo Checkers, this route grabs the bubble and also takes the easiest route under the boss fight. The second piggyback is not required, and you can swap to Marbles after the dropdash and before reaching the goal.

Intended

This is the dev's originally intended way to skip the fight. It's actually quite fast, especially since swapping isn't required. Simply knock Lunosa out with the shell before touching the boss fight platform to spawn the boss.

Checkers end

Instead of swapping to Marbles and shell jumping, it's possible to keep Checkers in front and do a normal quad jump to reach the goal. This usually requires at least two failed dropdashes, and combined with the fact that Marbles is needed for the next level anyways, this route is slower. However if you are comfortable chaining failed dropdashes it's potentially safer, as failing to get enough height with Marbles cannot be recovered.

Aim for a time of 6-8 seconds, depending on what strat you choose.