I'm trying to make a group of humanoids terrifying, imposing, dark. I need tips. They need to be a terrifying as Nazgûl.
Empty space. It's the ominousness of the impending and all powerful unknown that scares. Let the reader fill in the blanks - let their fear do the work. In the case of the Nazgul - it was't their description that made them terrifying but the effects they had on people - cowering in fear, abject terror, unable to mvoe and so on - essentially they were little more than invisble guys in cloaks. Likewise, Alien by AD Foster - the creature isn't really described until quite late in the piece, its the suspense around it that makes it fearsome. Not saying it's easy.
Well it depends on in what way you want them to be terrifying. If you mean instilling fear from appearance, then you have two options. One is the over-the-top guy wearing armor made from the still living (and screaming) faces of his enemies as blood drips from their empty sockets. The problem with directly showing stuff in literature (as opposed to simple special effects failures like in movies) is transforming the whole affair into gorn. Too much gore, or poorly written gore, and it is comical. The other option, useful in novels where the readers imagination can take control, is of course keeping description simple or never showing the guys. This can be done well. If you really want terrifying characters, then make them CHARACTERS with unique sytle/persona. Anyone can kill or torture the hero. Not everyone could abduct the hero's parents and flay them alive, eating the flesh with fine wine and a candlelit tabletop of course, while he watches the chained hero's expressions. Maybe ask him whether making his loved ones targets was worth the glory. If you MUST have physical stuff, then remember that humans relate to characters an ENORMOUS amount via facial expressions. Take away their eyes and lips, or make those features thoroughly inhuman, and a creature becomes "other" in the human mind. Put their mouths in their chests (or directly over the stomach) or in the hands. Creepy.
I agree that this is usually the best way to convey the terror of demon-like creatures. As a reader I often find descriptions of individuals, human or demon, rather lost on me. As long as I get the usual, hair colour, eye colour, maybe one key characteristic - overly tall or stocky - and that's enough for me.
Yeah I think elongated descriptions imply you've got time to stand around looking at one, which makes them less scary. I think glimpses followed by dramatic (but not too lengthy or elaborate) descriptions of the horror they induce or the havok the wreak work well. Or do what Lovecraft does and work the horrified reaction into the description, so for instance instead of having a face they might have a sickening, contorted mass of skin and gristle. Which is of course also what we have for a face but it sounds less scary when it's not described like that. Be careful of overusing that though, I got a bit tired in At the Mountains of Madness when he kept going on and on about things that were clearly just everyday objects as though they were some kind of crazy alien thing that his brain couldn't comprehend. Also bear in mind that, like children, the things we seize upon that come back to haunt us don't necessarily have to be 'conventionally' scary. Any casual detail, like being thin, or having large eyes, can be nightmarish if it's presented correctly. And don't focus too much on the visual - when it comes to visceral fear, smells and sounds can be much more powerful. A good trick is having an enemy make a characteristic noise (or smell) - that way the characters can know they're in terrible danger without being able to see where the threat is, which is terrifying on an instinctive level.
When you're walking in the dark, what scares you more? What you see or what you think you see? Everyone's points are the way I would go.
