Value: 2CP per rank
You respiratory system processes something other than oxygen. In Earth-like environments, you require a filtration system or portable atmosphere supply, as well as a sealed private refuge away from Earth-standard atmosphere. You can decide what you do breathe. This Comp is incompatible with the Need Not Breathe power.
Rank 1 (2CP): Normal nitrogen-oxygen earth air is inert gas for you. Breathing it causes no toxic distress, but you can smother in it the same way a human can smother in carbon dioxide. Apply drowning rules if you find yourself in an oxygen atmosphere without a filtration mask (same purchase DC as a gas mask) or holding your breath.
Rank 2 (4CP): Oxygen is a metabolic poison to you. Exposure to oxygen atmosphere (once you stop holding your breath) counts as a poison attack, save DC 18, 1d6 Constitution damage for round of exposure. Thus, you suffer both asphyxiation and poison effects at once. Ability damage lingers if you survive the asphyxiation effects.
Rank 3 (6CP): Oxygen is a virulent metabolic poison to you and an irritant to your mucous membranes. You must not allow any part of your face or respiratory system to come into contact with it. Even momentary exposure to oxygen (regardless of whether or not you hold your breath) counts as a poison attack, save DC 20, 1d6 Constitution damage for round of exposure. Exposing your eyes requires a Fortitude save DC 20. If you fail, you are blinded for as long as you’re exposed to oxygen, and for another 1d6 rounds afterwards. You must make these saves versus poison every round until you leave the oxygen or start taking damage from it.