I love it when there's no way to fight a certain monster, and it's the one causing fear. The fact that youre helpless and the only thing you can do is run
Rayman 3 did this in the Desert of the Knaaren level, where there were these flesh eating mummy-zombie-esque creatures that would slowly chase you, but were invincible. While the overall design of the level was different than any other stage because there was no music and it was creepy. It was totally unexpected.