EDIT: UNFORTUNATELY, AFTER PATCH 1.0.6 OF THE GAME, AIR SWIM IS NOT A WORKING GLITCH ANYMORE

Air Swim was found by Zeldrene. Your character continues swimming in air after getting to the surface from underwater. Air Swim is used in Shadow Fish Lagoon (approx. 45 second timesave) and Pump And Dump (approx. 30 second timesave).

Below is the guide on the Shadow Fish Lagoon Air Swim. Pictures and videos by Zeldrene!

You approach from the left as normal. Imagine 3 zones (picture below). After you get into zone 3, keep going until you deposit the fish, and turn around. Go back into zone 2 and turn around again in the narrow vertical slice (picture below). MAKE SURE TO NOT TOUCH ZONE 1!

From this point forward, the setup is done. Swim out of the water, and you'll keep swimming in air until you re-enter water or die. Keep swimming upwards until you get above the level, out of bounds. Swim to the right until you see a red line (picture below), which is located above the level exit. Go down from here, touch the end trigger and finish the level.

Here's a video of the setup:

Here's a video of the entire level with Air Swim: