3 Dark Side Skips

From SMO.wiki

The 3 Dark Side Skips, abbreviated as 3DSS (which is a pun on 2DSS), are three skips all performed in an identical manner that allow the player to skip the Topper, Spewart, and Rango boss fights in Dark Side by bypassing the trigger areas that initiate each fight. This trick saves a large amount of time in speedruns that complete the boss rush, and was discovered jointly by Mars2030, MiiWii, and Sledged_Hammer.

The trick cannot be used on the second floor of the tower to skip the Hariet fight, since unlike the other three floors, there is an additional trigger zone that completely encloses the exit loading zone, making it impossible to leave the room without initiating the fight. However, in two-player mode, there is a faster method to skip the fights by scaling the tower from the outside, known as the 4 Dark Side Skips, that bypasses all four fights.

Explanation

The trick can be performed by vaulting to the right of the arena, falling almost down to the poison, doing a homing cap throw, downthrowing, bouncing off of Cappy, wall jumping, and then diving onto a sloped surface on the wall to cancel the dive, then wall jumping once more, doing another homing cap throw, then diving into the back side of the arena. From there it is possible to jump to the exit door.