Alirght, I'm gonna go through the things we have known about the Aliens, from watching the movies and I added the info from AVP-R:
ALIEN (TR/DC):
-Alien eggs. They are oval and open up, via petal-like flaps at the top, when movement/host is detected. They are also transparent, when lit.
- Facehugger - Looks something like a crab. Emerges from the egg and attaches to host, by clasping it's claws around a host's face/wrapping tail around neck, implants embryo and then dies.
- Acid is the blood of the creature
- Chestburster - Infant Alien that is like a serpent. Bursts from host's body, after a number of hours, and qucikly slithers away. NOTE: Hands and arms of the burster were removed, before filming
- Skin sheds/Alien becomes full-grown in a matter of hours
- Alien appears biomechanical, with a exoskeleton, is able to stand and walk bipedial (but is also believed to be a quadriped, as shown in behind the scenes footage) has a smooth dome-head, tubes sticking out of its back, spear-tipped tail (apparently, used to either kill or paralyze it's victims), inner-jaws attached to a tongue (to instantly kill it's victim, with one strike through the brain)
- Alien likes to hide in dark places (tunnels, basements, etc) and preys on its victims with stealth (appearing behind the prey from above, sneaking up on them, etc)
-Alien is also able to blend in with it's environment
-Alien is able to cocoon hosts for egg-morphing, as a survival method to keep the reproduction going and the apparent explaination of how the eggs are created.
ALIENS (TR/SE):
- Introduces the riged heads of the Aliens, as a possible sign of age or it could be a design choice by the filmmakers
- Chestburster is seen with arms/hands
- Aliens crawl and climb on walls/ceilings and are able to swim
- Alien drones create a hive and now, the creatures are more like a colony of bees or ants
- Aliens grab hosts/cocoon them in the hive to be used for face-hugging
- Full-grown Queen Alien is introduced. The Queen appears imobiled on a egg sac, which lays the eggs. NOTE: Possible that this may also eliminate egg-morphing theory, unless this is just another alternative method to keep the cycle going.
-Alien drones stay around and "protect" the hive/Queen
- Queen is able to be detached from egg sac and run around freely, when threatened
-Queen moves very fast
-Queen uses tail to impale enemies
ALIEN 3 (TR/AC):
-An egg on the Sulaco suggests the Queen layed one final egg, without an egg sac
- A normal facehugger apparently throws acid on a cryotube and attaches to either Newt's or Ripley's face, before the Sulaco pod crashes onto Fury
- The same facehugger is still alive, after impregnating Ripley (Goes against the idea that facehuggers die, after implanting a host). NOTE: In the Alien 3 comics, the facehugger implanted the embryo in Newt, but during the crash, the chestburster crawled into Ripley's mouth.
-In the TR of Alien 3, the same facehugger attaches to a dog and the "runner" chestburster (quadriped) is born
-In the AC of Alien 3, the Super-facehugger is introduced and attached itself to an ox and the same "runner" chestburster is born. NOTE: Where was the Super-Facehugger egg?
-It is also confirmed that the Alien will take on the characteristics of it's host (in Alien and Aliens, it was unclear if the look depended on the type of host or if it was natural for every Alien)
-While still maturing, the Alien is able to spew acid from its mouth (more like vomit), as a defense method (i.e. Murphy scene)
-The Alien design has the creature with a smooth head and running around as more of a quadriped, without the tubes on the back
-The Alien is VERY fast
- The Queen is able to be born via chestburster
-Aliens will not kill hosts with chestbursters (possibly, because its just a Queen)
-Queen chesbursters have arms/hands and a crest at birth
ALIEN RESURRECTION:
-Queen rapidly grows and while in containment, it is able to produce eggs
-Aliens have no problem sacrificing one of their own to survive
-Aliens are seen swimming like iguanas, with a more flat/fin-like tail blade
-Aliens still have smooth heads and gain back the tubes on their backs, but now the design is that the creatures have bigger chins/more sloped dome
-Aliens spit a stream of acid (more projectile than the Alien3 creature) in the faces of their prey
-Facehuggers are seen leaping a great distance from eggs and onto their victims
-As a strange effect from the human cloning, the Queen is given a second reproductive cycle, which is to give birth (like a human) to a 'Newborn" (half-human/half-Alien hybrid)
-A normal chestburster has no arms/hands, but the design of the creatures head is different than previous films.
AVP: Alien vs Predator:
-The Aliens are given a special hormone, from the Predators, in order to speed up the cycle procress (which is not explained in the film, but by the director) and thus, the chestbursters are born in a matter of minutes and not hours
-Facehuggers are seen leaping a great distance from eggs onto victims (even more than Alien Resurrection)
-Chestbursters still have no arms/hands
-The Aliens can survive in very cold temperatures
-The Aliens retain the smooth head and tubes on the back, but loose the flat tail
-The Aliens can now claw at their opponents with their fingernails, as well as stab them through the chest with their spear-tipped tail (as indicated in ALIEN and seen in ALIENS with the Queen)
-The Queen still moves REALLY fast
-The Queen kills the "Scar" Predator, even though he has a chestburster
-PredAlien chestburster emerges from the dead body of "Scar", with the mandibles
ALIENS VS. PREDATOR - REQUIEM:
-PredAlien is either born a Queen or molting into a Queen. Idea is that Aliens will molt into Queens, when there is no Queen present. NOTE: Possible that this may also eliminate egg-morphing theory, unless this is just another alternative method for Alien drones to keep the cycle going.
- Assuming the PredAlien is a born Queen, this will be the first time a young, free Queen (between chestburster and full-grown, egg laying adult) has been seen on film
-New reproduction/survival method for the Queen is introduced (when she is young and roaming around freely), the Queen is able to "regurgitate" embryos (unsure if it's a liquid vomit substance, a tube to pass down the throat, or chestburster body passing) into hosts. Method used, to (possibly) create quick Alien drones to be used to construct a hive/protect the Queen, so she can settle and start mass producing eggs via egg sac
