Disclaimer: This is speculation based on available knowledge from the Grimoire. Cabal Cabal physiology is comprised of leathery skin that requires a highly pressurized humid environment. They are tall but considerably heavy in terms of fat and musculature. They have one row of razor sharp teeth suggesting they are carnivores though how much Terrestrial based taxonomy applies to an extra-terrestrial species is unknown. Psions are smaller than average humans and very frail. Their suits do not seem to be as heavily pressurized due to no explosive decompression on suit breach. Their light bipedal physiology suggests a low gravity homeworld that coincides with their suits lack of heavy pressurization. We know the Cabal are an interstellar empire and that the force we are fighting is a scouting/expeditionary task group sent to either expand into our system or investigate it. Cabal follow their orders to the absolute letter. The only contrary example we have are the Broken Legion. It seems that their Empire mandates that either you successfully conquer a region of space or remain exiled. Concerning their penchant for planetary annihilation. The Cabal Empire itself appears to be afraid of something. Since their homeworld is a high gravity jungle planet (I've come to these conclusions based on their biology) they build things big. This makes sense because flimsy construction would be impossible under increased stress. Alternatively this could be because they fear something. The Hive. The Hive burrow into worlds for breeding grounds. The Moon is the perfect example of this. The Cabal may destroy celestial bodies as a sort of scorched earth policy. Asset denial. Psions are a vassal species. Their radically different biology most likely means they come from a different world. They are also incredibly intelligent and possess some form of seemingly psychic ability. What makes this interesting is that it's independent of the Light or Darkness. I say that last bit because they attack both us and the Hive. Not to mention they do not perform rituals or seemingly worship gods as evidenced by the Vex and Hive. Also of note is that their culture has no term for ghost. They are aware of our AI companions however, and know they make us virtually immune to attrition based warfare. They recommend investigating the Hive's anti-ghost capabilities. This could lead to relation with the Darkness later but the status of the group responsible for the recommendation is likely dead. Due to the mission "Outbound Signal" it is almost certain a future DLC will cover them in greater detail. Eliksni (Fallen) Eliksni are bipedal four-armed humanoids with insectoid/arachnoid physiology. As such their growth rate is very flexible and they regrow limbs with ease. They are incredibly agile and have little trouble traversing rough terrain. They live off of a substance called Ether which seems to be inherent in all matter as their Servitors are machines designed to convert matter to ether. This also adds credence to their looting tendencies and machine-worship. We know the Traveler (they called it the Great Machine) uplifted them in a similar manner to us. Their homeworld was described as a world with pink skies and was beautifully lush like Earth. We also know their society was broken into various Houses. What House organization is based on is unknown but it most likely had to do with various tasks and assigned duties. The Houses we see today are shadows of their former glory and may not follow their original tasks. We also know of two deceased Houses: Rain (religious) and Stone (creation/construction or leadership?). Fallen society was destroyed in an event called the "Whirlwind". The Hive attacked them with overwhelming force. They only survived due to a confrontation between Savathûn and Oryx, but not without being nearly wiped out. They live in a tiered society, but this may not have always been the case as mentioned by Variks. They may be an example of what would happen to us if we followed Dead Orbit's wishes. Of note is Variks. His plan to become the Kell of Kells could lead to an alliance situation similar to the Elites from Halo later. Vex We know they are biological in nature. They exhibit psychotropic capacities in alien biology with the chief example being Kabr. This may hint at them being a species of evolved microorganisms. Or it may simply be some form of technology. They were once organic creatures that most likely experienced a technological singularity and opted to trade their frail physical forms for machines and share a hive mind. They are trans dimensional so many aspects of them may be incomprehensible to us, and us them. We know they seek to create a favorable end state for every possible outcome of the universe thus making them impossibly more advanced than us. But since we still exist it may be that we are more aligned than adversaries. It is also of note that they do not necessarily kill off life in a region they control. Mercury still has a breathable atmosphere. It is also of note that they do not follow one mind implicitly and exhibit independent functionality as evidenced by Quodron and it's followers. We know the Vex worship the Darkness but this may be an independent group foreign from the greater Vex network. Quria was the mind that originally contacted the Darkness via a portal to our dimension created by Crota, Son of Oryx. It failed to kill off the Hive and may have been a reason for stopping all Vex from worshipping the Darkness. They may also simply all follow the Darkness but have not been given god-like powers, but Oryx never mentions them as followers of the Worms, and the Darkness seems ambivalent to them. They may just be a curiosity. Vex have one imperative: construction. This is the basis for all Vex platforms with combat being secondary functionality. This also goes against the Darkness' grand design which I'll get into later. They apparently believe in beauty as well, as constructs with limited function beyond looking good have been observed.