Hot water

Hot water, also referred to as gelatin, ooze, or green slime, is a type of toxic green goop that appears in Super Mario Sunshine. Despite its name, it bears little physical resemblance to ordinary water, being a viscous green slime. It burns Mario on contact, dealing damage and causing him to be thrown up into the air as though he touched fire or burning goop, and unlike many kinds of goop, it cannot be cleaned by water shot by FLUDD.

Hot water is only encountered during the final boss battle of Super Mario Sunshine, during which Bowser and Bowser Jr. are seen soaking in it unharmed in a gigantic hot tub located at the peak of Corona Mountain. They both remain in this goop for the duration of the final battle. During the battle, Bowser sometimes ground-pounds the hot tub to splash the hot water on Mario and damage him. There appears to be an unlimited amount of hot water in the hot tub; when Bowser tilts the tub, most of it falls out, but the supply is immediately replenished. After Mario ground-pounds all five sections that branch off from the hot tub, the entire hot tub tips over, and all of the hot water falls out of it into Corona Mountain. The large Shine Sprite that was trapped in the hot water is also set free.