Oxygen

Oxygen is a gas that is apparently poisonous to Hocotatians such as Olimar. It is unknown as of yet what gas Hocotatians breathe on Hocotate.

Effects
The effects of Hocotatians breathing it in are unknown, but at some point in the process they die. Olimar can be seen in Pikmin to have died due to inhaling it during the Bad Ending cutscene.

Jetpack
The Jetpack in Pikmin:Doomed Time converts this and Nitrogen into thrust which can then be used to fly.