The most scariest enemy

[LoneWolf]

Honestly I still perceive the Shadow as the scariest being in Amnesia. That characteristic echo sound, combined with that

Spoiler below!

climactic chase at the end

really makes you feel like the Shadow is a disgustingly large and powerful force.

Yeah until you look at the script, or play that scene a few times over.
You will realise that-

Spoiler below!

The entities and sounds and dead area.. blah blah blah... (Basically what makes up for the guardian its self) goes faster the faster you go, so if you run it will go fast, if you stop for a moment it will slow down. So you cant ever die unless you barely move or dont move at all. So if you run you will survive even if you make the wrong turn, as you will notice it slows down at that point sadly being able to see the scritping and understanding it kinda ruins the game, but good thing i played through it alot beforehand.