Michael's utter relentlessness in pursuing Laurie. It perhaps doesn't top the Nothing Is Scarier nature of him possibly targeting anyone, like in the first film, but the fact that Michael simply won't stop is utterly terrifying, and even prompts Laurie to ask why he won't die, at one point.
Going along with this, the shot of Michael walking on fire before he dies. It's just so creepy to watch Michael be so determined to fulfill his objective that his imminent death doesn't faze him.
If you get nervous or scared in hospitals, this is not the movie you should be watching.
Doubles as a Tear Jerker- the Michael doppelganger getting hit by a police car, and pinned between it and an ambulance which suddenly explodes. Made worse by the fact that said person was just an unassuming regular. If only Loomis had paid more attention to the hair colour on the mask...
Laurie and Loomis being trapped in a small room with a blinded Michael Myers swiping erratically with his knife. This also applies to the shot of him bleeding from the eyes in the same scene.