From this trailer I have a feeling I might know what one of the gameplay mechanics will be. I'm guessing that when you travel into an area with these invisible creatures you will need to rely on stealth to avoid them, including a mechanic where you'll have to hold your breath, but since they're invisible you must rely on either one of two things to know where they are. First is the sensor on the back of the suit Reedus and that other guy had, the other is simply looking at the oily footprints they leave behind. The trailer also made me think that those babies in the pods actually might be some kind of power source as I noticed that the sensor on the back of Reedus' suit only activated when he picked up the baby the other guy had after the guy got picked up into the air by the strange giant creature.