So The Engineers are no longer accepted in the world of humans. Maybe one was killed or attacked due to 'aliens' being against God or something but The Engineers were not going to settle for it. In their 'labs' they further push their tests of Human DNA and discover the perfect weapon or at least something that will use humans as a host and the result would wipe them out. Judging by the room with the giant head, the head looking down on the evolving creations in their capsules, the combination being created could be the basic ingredients for the alien we all know and love (let's call them Xeno's to make this easier to read). At first I felt the Engineers worshipped the Xeno form, given the giant mural dedicated to it but I don't feel that's the case any more. Given the fact their moving murals indicated the balance in the room, the Engineer's science is a beautiful thing and not flashing lights and computer screens. I now feel this large Xeno mural is essentially a blueprint or if you want to put it more basically, a label or poster depicting what the glowing green container at the front of the mural holds. The genetic code they use to splice with their own batch of nasty in order to unleash the perfect exterminator of life on Earth. Of course this is held in high esteem, it's the Engineers ultimate get out clause. It cleans up their mess and the dangerous nature of the beast is something not to be taken lightly. Delving deeper, this changes however. Let's look at the evidence. Humans mess up the balance of the giant head room just by being there and things start to change. Even with the simple moisture from the human guests as they enter the room, the fine balance of DNA in the capsules begins to change. What's brought to life is an early version of the Xeno or more specifically the system to get the required DNA into a host's system. That system's ultimate evolutionary result is of course the facehugger. The beasties we see all share the same characteristics. Beasties with tails to strangle and squeeze and want you to open your mouth. They want to get inside of you and even though cobralike xenos just want to attack, attack attack, what they're swimming in, and what caused the problems on LV-223 seems to mess up Human/Engineer DNA in a big bad way. Holloway gets one drop in his drink and he starts react. We don't see where the infections leads fully but he does show signs of aggression and enhanced strength. Fifield falls face first into the stuff and the next time we see him, he's strong, able to bend his entire body over at ease and comes close to taking out the crew of the Prometheus single handed. More rage, more anger, almost as if the black goo gives the hosts the attitude and abilities of a Xeno. Attack, attack, attack. The last visible sign of this infection is in the head of the Engineer found inside the big head room. Electro fitted back to life, we witness the final stage of this infected space God. His head swells, his DNA changes and boom. Explosion. So this may change what we assume the Enginners plan was. They were not looking to implant Xeno's into the human race but they seem to be using their DNA to mess with ours. Given their cargo is literally hundreds of these ready to go capsules full of Xeno spliced nasty goo, as opposed to xeno eggs. Their end game was just to use what they'd derived from Xenos. As opposed to the Xeno's themselves. On a side note. We know, they know the Xeno's exist, as per the mural but whether they created them or simply had an encounter with them in the past is a much larger question, not covered here at all. That said I can take a gleeful Alien smile at the fact that essentially the real menace here is the Xeno we know and love, just in a liquid form. They still manage to mess things up, even if indirectly (and this strengthens the idea that this is a prequel, not just a passing nod to Alien).