Natural gas

Natural gas is a sometimes helpful, sometimes harmful hazard that takes the form of various-colored gasses seeping from the earth through cracks in the ground or from enemies or plants. While these gasses dissipate in open-air environments, they linger in underground chambers that have no ventilation, and when inhaled, may cause various effects such as changing the properties of certain enemies, plants, and Pikmin. While natural gas in itself is not life-threatening to those that inhale it, its effects often result in dramatic changes to common strategies.

=In fanon games=

In Pikmin Evolution
Natural Gas is a rare hazard that appears in Pikmin Evolution, only appearing in a select few dens. It takes the form of a thick blast mist, resembling a light layer of smoke. Natural gas mainly comes out of vents in the ground, while outside the gas dissipates, inside it can clog up and form a dangerous air-born substance. Natural gas is made of a mixture of methane and other foreign particles, which makes in poisonous to both Leaflings and Pikmin who breathe it in. When a Leafling, which is the species that make up our captains, inhales this gas, they will have their health slowly sapped away like a poison-esc damage over time effect. Speaking of poison, any Pikmin that enters areas heavy in natural gas will be poisoned, meaning they can't enter gas-filled areas. That is unless they are a Roach Pikmin, as they can breathe it the natural gas like normal and even create an air shield around the captains with their wings, slowing down the health degradation effect of natural gas. Natural gas is usually cleared by activating a nearby fan, which helps properly ventilate the area and makes it easier to breath. However, some rooms don't have this luxury, meaning you are stuck dealing with natural gas and have no way to remove it. Luckily natural gas only appears in a few dens, those being the Smoke House, Titan's Dream, Dingy Nest, and Dragon's Den, so it isn't a super common hazard to come across.

In Pikmin: Spark
Natural gas is a nonlethal hazard appearing in Pikmin: Spark, taking the form of a foggy, colored mist emitted by some enemies and plants or seeping from cracks in the ground. Normally, they simply dissipate in the atmosphere, but in underground areas such as the Cavern of Cobwebs, Rust Labyrinth, and several dens, they can quickly fill up a room and affect general gameplay. The color of natural gas determines its effects when inhaled: red gas makes Pikmin heavier, meaning they can't be thrown as high, but they and their predators are much faster; green gas makes Pikmin be able to be tossed higher, but they and their predators become slower as a result; white gas doubles the attack power of Pikmin but halves the defense of captains and enemies; lastly, purple gas doubles the defense of captains and enemies but halves the attack power of Pikmin. Natural gas can be cleared by opening vents, allowing the air to be better filtered.