Year 2000, 8 years old, playing Medievil with a friend. I had already played the demo so I wasn't expecting anything to scare me at all, but as the intro rolled along, I saw Zarok's ugly face upclose during the FMV, and couldn't forget it. Luckily, I wasn't a scary child, so in the end it only helped me develop some of the "healthy" human fear our brains need to function properly but, hell, it took months to not think about that face at night.
Also, one evening I was in the garden with my family and some friends of ours, and my dad asked me to grab something inside our house. In the meanwhile, he was telling our guests an old story about a friend getting hurt lightly and in a comical way, but all I could hear from inside the house was just dad mimicking his friend's pain moan ("Bluuurgh"), which drew me to the conclusion that Lord Zarok had arrived, and I was screwed. I could only crouch and put my arms around my head, I started calming down only when my mum started calling because I wasn't coming back. Getting back outside felt really like an endless trip, and I was really surprised to see everyone safe and ok while i finally got outside.