Anyone who has A) played Destiny and B) can aim will know that the Fallen, upon cranial expiration, will explode in a shower of a substance called "Ether". They are decidedly addicted to this substance, using Servitors to collect energy and even cannibalise the dead in order to create it. This flammable, addictive, pale, and (according to the Grimoire) pungent liquid also, supposedly, keeps the Fallen alive and grants them both the blessing of strength and the curse of their feral nature. My theory is this; that Destiny's "Ether" is a version of a real chemical; Diethyl Ether. Let's start with the most visible quality of Ether; flammability and explosiveness. Diethyl reacts explosively with chemicals in the air at high temperatures, the kind that might be provided by a headshot. This raises the question of why the Fallen aren't just exploding randomly, but I'll talk about this later. About its appearance, Diethyl is a colourless liquid under most circumstances which matches the pale Ether blood often left by dead Fallen. Another, lesser, point would be the powerful, sweet scent also left by Diethyl, something echoed by Varik's' scenes in the Grimoire where Ether fills the air. Which brings me onto the seemingly unexplainable addictivity and strength-enhancing abilities of Ether... Or are they? Ether-addiction in real-life exists; etheromania, a condition often associated with the drinking or INHALATION of ether. The Fallen do this through their masks, and given Diethyl's solvent nature, it might well help to serve as blood for the Fallen. Ether being Diethyl also explains how Servitors even produce the stuff; it's just carbon, oxygen and hydrogen reacted together, gathered, often from corpses, and then combined with energy from elsewhere. As for the strength, size and resistance it offers, while the former two are hard to pin down in a sci-fi so filled with space magic and wizardry, the latter is easy; Diethyl Ether is a narcotic, an anaesthetic, the Fallen don't feel much pain because the Ether softens it. Going back to why the Fallen aren't just exploding everywhere, they likely, as a species closely related to insects, have cold blood and a cool internal body temperature. So, at the end of the day, the Fallen aren't space pirates surviving on magic and plunder, they're just junkies looking for their next huff of Diethyl Ether.