The Phatgas seem to thrive off the fumes that are excreted by the volcanic mountain upon which Heelspike is seated. These creatures bodies are like great balls of gas and they float around above the city, slow and ominous. They are however harmless.
They are used like blimps by the town guards, who at night float over the city shinning a light from a basket suspended below the creature which briefly illuminates the dark alleys and back streets of the city looking for those defying the law.