Mr. X from Resident Evil 2 in the B Scenario. When he is initially dropped down on you, you're like, OH, a boss for later! Then, he's right there in front of you, and if you run, this mofo breaks down the wall to come get you. That is the scariest moment in any video game ever. Also, there's a part where a Licker breaks through the glass and it makes me jump and freak out because they're tough if you're not equipped right.

Pyramid Head battle in the labyrinth is also intense because you have to see him multiple times if you don't know where you're going. It just adds to the intensity.