Gills

 is a buff granted to the player upon consuming a Gills Potion. The buff forces the player to breathe water or lava instead of air. This last for 2 minutes, but can be cancelled at any time by right-clicking the icon. When in air, the player's Breath meter will slowly deplete, making this more of a double-edged sword than a buff.

Trivia

 * Equipping the Fish Bowl in your armor slot allows for normal breathing on land with this buff.