Alex arrives on Earth some time ago to act as a scout for the aliens. It is unclear precisely what she was doing during that time, although it is likely that she was attempting to gather intelligence on the human race, while also satisfying her species' desire to reproduce. In the beginning of the film a pizza delivery boy arrives at a house to find several frozen dead bodies of men, and at the end of the film it is revealed that they were killed by Alex herself, who appears to know the pizza boy. She tells him he's late, and then presumably rapes and kills him, too.
Events of Decoys
Alex congratulates Luke on his victory over the aliens, and takes him back to her apartment. There, the two of them profess their love for each other, and Alex allows Luke to undress her. It is shown that Alex has no bellybutton, implying she is an alien.
Luke lays Alex down on the bed, but Alex immediately wraps her legs around Luke, then pushes him down onto the bed and straddles him. She then tells Luke that, now that the others are gone, she can finally have her way with him. She then pushes Luke down and straddles him Flashbacks reveal Alex was the one working behind the scenes to disrupt Luke's attempts to stop the aliens.
As Alex begins to ride him, Luke realizes too late what's about to happen. He cries out and attempts to push her off, but Alex easily overpowers him, pinning his arms down and continuing to thrust her hips against him, arousing herself. Luke screams as Alex continues to ride him, finally releasing her tentacles. The camera zooms out of the room, showing Luke still screaming as she rapes him. Luke's fate is left unclear, although he is presumable impregnated by Alex.