Having watched a series of movies involving aliens that hunt and kill humans:
They tend to breath air, water and vacuum.
They seem to be immune to -700 degrees and +400 degrees when in space but can sometimes be burned by torches.
They eat humans even though they are totally alien tissue composition.
Bullets either can not seem to hit them, tend to bounce and if they do hit, they do tiny amounts of damage.
They can see in total darkness, blinding light, infra red and just about every spectrum.
They do seem to be able to shift shape to smaller than their normal shape.
Have beam weapon technology, that when fired can sometimes be dodged as the energy beam is no faster than a slow bullet.
Traps, no matter how cunning are spotted or avoided easily except the last one, which is typically never fatal.
Aliens are Asexual, leaving young here and there when there was only one to begin with.
Aliens can use human females to reproduce with, or speed the incubation of their eggs with.
Loss of a major limb is never fatal, just slows it a tiny bit.
Repeated shots to its head that splatter plenty of goo and gobs of flesh are not typically Final fatal.
Alien demolition charges to cover up their presence always have a countdown timer, especially the self carried ones... for some reason.
Can you add more?