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 Pump and Dump Air Swim. Pictures and video by Zeldrene!

Air Swim in Pump and Dump works in a similar fashion as the one on Shadow Fish Lagoon. You approach from the left as normal. Imagine 3 zones (picture below). After you get into zone 3, turn around, go back into zone 2 and turn around again in the narrow vertical slice. 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 above the level, until you get to the final water of the level. Re-enter the water here, and finish the level like you normally would.

Here's a video of the setup done on Shadow Fish Lagoon, which works with a similar idea as the one in Pump and Dump:

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