Reading Star Crawl, and I thought about this as I went through the race section.
Gas Creature: Some creatures are not beheld to a body. They exist as a creature of pure thought and molecules. These intelligent gasses are far harder to hurt then the simple protein based bodies of their kin, but lack the physical form to do much heavy lifting.
Stat Adjustments: Strength -2; Intelligence +2; Hit Die -1 Step (min d4)
Special Abilities: Gas Form (physical damage is reduced to minimum for all attacks), Space farer(does not need space suit in areas of no oxygen and is not harmed by environmental extreme cold or hot but take normal elemental damage from weapon, attack, or spell)