I like the giant toy soldier scene the best
Everyone remembers the graphic, stomach-churning scene of the woman in the cottage giving birth to a full-grown man the most, but then, everyone remembers their worst nightmare the most.
However, given the choice of favorite (not necessarily the best) XTRO scene, my vote goes to the scene where a full-sized, animated (android?) version of the boy's toy commando soldier appears at the nasty old lady's door. The android-like, human-sized toy commando soldier looks even more toy-like than it's original 12-inch version. It walks with a stiff, shambling gait, like a first-generation android.
The killer android toy commando soldier figure somehow has all the right tools it needs at the moment. It sticks a handy bolt-cutters into the door to snip the metal security chain. Then the android toy commando sticks an explosive disk to the door, blowing it open. But when it became a human-sized android, from it's original 12-inch toy version, it's M16A1 rifle was still a toy even though it was a real-size M16. Nonetheless, it's attached bayonet is now deadly steel. The toy commando soldier stabs the old lady to death.
I liked this scene because of its pyschological connection to toys and childhood in my mind. I even checked eBay to see if I could get my hands on a replica of that 12-inch toy commando action figure. I intended to place it at my work desk, using it as a conversation piece to open talk on science fiction movies.
The actor who heroically donned the uncomfortable latex skin for the toy soldier commando android went by the name of Tik in the credits. What kind of name was that? The monster was played by an actor going by the name of Tok. Great sense of humor there.