that scp-096 scream when lee dies was perfect.

Sounds like the background music of a horror game.
Set deep down in the suburbs, you are tasked to find the missing totem of light before you lose sanity. Or something like that.

Cons: ending is too abrupt, have it lead out more, get quieter at the end, etc.
Dont be afraid to sound a tiny bit off key when doing dark ambient, sometimes it makes it more scary.