I nominate Macabre's Sinister Slaughter.

Bell Witch's album Mirror Reaper has a very spooky sound

Qrixkuor is pretty scary, but doesn’t really compare to Portal like mentioned above. I really like that Veilburner’s albums all sound like performing a ritual to see through the veil and then losing your mind.

Any Portal, but I always go back to Vexovoid. It’s death metal.

Also Thantifaxath - Sacred White Noise is probably ‘scarier’ but Hive Mind Narcosis is really good too. ‘Avant-garde’ black metal.

All the Vermin Womb for some grind-based ‘scary music’.

Saving for later :D

I wouldn't call it scary but Embrace of Thorns - Praying for Absolution has a strange atmosphere and vocals to me.

Murder by Gehenna.

How is sunn o))) not mentioned? Is that not considered metal? Because I refuse to believe that black one isn't one of the scariest albums ever made.

Csejthe by Mordor is atmospheric, slow doom album to listen alone at night.

https://www.youtube.com/watch?v=sppnGzr1IdQ