Any1-4

Optimal

This swimming level can be completely bypassed by clipping through the ship - reducing the length of the level from around 47 seconds to just 12. It is possible to end this level with either character, depending on where you want to clip in Salamancer's Sanctum.

Marbles end

The easiest way to clip in this level is by using two dedicated binds to wall clip. Using the fact that two keys can be bound to one action in the in-game bind menu, bind one button to both left and piggyback (this will be used to set up the clip), and another to both right and tagteam (swap)(this will be used to execute the clip).
To clip into the wall, land in the corner next to the wall and press the "setup button," followed by the "clip button." Make sure to touch the wall to stop moving before pressing the setup button, or you will not turn to the left and will need to press left manually.
If you don't go through the wall, it usually means you were too far away. Wall clips only work if you are right next to the wall.
To clip back inbounds, land on the platform above the bonus and repeat.
Using a team attack to break the piggyback is faster than un-piggybacking, as it requires only 16 frames instead of 30.
Going in the bonus will take you back inbounds, but loses about 2.5-3.0 seconds.
You can save a few more frames by going over the barrels at the end instead of rolling through them.

Checkers end

This strat puts Checkers in front for Salamancer's Sanctum in preparation for the closer cip.

In order to cross the water without landing in it, you must enter the wall from higher up. To accomplish this, roll off the ledge, piggyback and jump to the wall. You must briefly tap left, then press your "clip button." It helps to do the second input immediately after the first.
Overall this strat is about 0.1-0.2 seconds slower. Your choice of strat should be based on which type of clip (in Salamancer's Sanctum) you find more consistent.