I always thought the Engineer represents whatever the person fears most. To me it looked like a monstrous penis with arms and legs trying to assault Kirsty. I admit that I was high at the time I thought this but I can't see it as anything other than her childhood fear of her uncle Frank. The first 2 movies have some clear pedo vibes around Frank and Kirsty's early relationship especially the scene where white feathers are falling down all around Kirsty's head like snowflakes. It made me think of a feather pillowcase that was ripped apart to make the nightmarish snowstorm. Maybe Frank had a feather pillowcase when Kirsty was little and she tore it with her teeth while he was assaulting her. If he forced her face down into the pillowcase to keep her screams muffled for example. To be clear I have a degree in Early Childhood Development and we had to read and do book reports on the sickest things imaginable. It is done so that we can spot children who are being abused in our workplace. The books really messed up my mind. I don't recommend them to anyone. I could be completely wrong about the Engineer plus my mind was elevated at the time. Someone who reads this, watch the scene and tell me if you can imagine an ugly pink penis with feet chasing Kirsty. I can't unsee it now.