"It was a figure no larger than a young child, but sere and shriveled as some millenial mummy. Its hairless head, its unfeatured face, borne on a neck of skeleton thinness, were lined with a thousand reticulated wrinkles. The body was like that of some monstrous, withered abortion that had never drawn breath. The pipy arms, ending in bony claws, were outhrust as if ankylosed in posture of an eternal dreadful groping."
Get that nasty adjective? Quachil Uttaus doesn't just grope. Its groping is dreadful. You have to imagine what that looks like for yourself.
Lovecraft used this technique to strong effect - sometimes in a way that strays dangerously close to self-parody, as in the description of Azathoth:
"That last amorphous blight of nethermost confusion which blasphemes and bubbles at the centre of all infinity -- the boundless daemon sultan Azathoth, whose name no lips dare speak aloud, and who gnaws hungrily in inconceivable, unlighted chambers beyond time amidst the muffled, maddening beating of vile drums and the thin monotonous whine of accursed flutes."
I'm not sure what a "vile" drum sounds like as opposed to a normal drum, or an "accursed" flute as distinct from a flute, but it certainly sounds worse.
What Lovecraft and Smith are doing here is providing a spur to your imagination. What's "dreadful" groping? Better to let the reader imagine just what that might be like, rather than try to explain. While these monster descriptions are florid, they operate on the age-old principle that often letting the reader's imagination do the work is the most effective way to scare them.
Over-exploit this technique, though, and you're in trouble. Think of Lovecraft's description of the Byakhee:
"Here flapped rhythmically a horde of tame, trained, hybrid winged things... not altogether crows, nor moles, nor buzzards, nor ants, nor decomposed human beings, but something I cannot and must not recall."
What does that look like? Fucked if I know. It's not so much a spur to imagination as a bucket of water thrown all over it. There are too few dots, and they are too spread out, to really join up.
Similarly, this technique can go too far. Lovecraft's later imitators often fell into the trap of simply telling you something was scary or horrible without really detailing why. From Derleth, describing Zhar, the Twin Obscenity:
"The thing that crouched in the weird green dusk was a living mass of shuddering horror, a ghastly mountain of sensate, quivering flesh, whose tentacles, far-flung in the dim reaches of the subterranean cavern, emitted a strange humming sound, while from the depths of the creature's body came a weird and horrific undulation."
Yeah, okay, we get it, it's a mass of shuddering horror, it makes weird and horrific undulations. We know because you're telling us. It's weak writing.
MR James wasn't averse to using a nasty adjective here and there, but he was at the opposite end of the spectrum - the Minimalist Description Approach. In MR James stories, you never properly see the ghost. It's always in the dark, or glanced at, or described by somebody who fainted and only dimly remembers. Often this method works best of all; James knew how to give the absolute minimum description necessary to get your mind racing to fill in the details. From 'The Treasure of Abbot Thomas'
"My dear Gregory, I am telling you the exact truth. I believe I am now acquainted with the extremity of terror and repulsion which a man can endure without losing his mind. I can only just manage to tell you now the bare outline of the experience. I was conscious of a most horrible smell of mould, and of a cold kind of face pressed against my own, and moving slowly over it, and of several - I don't know how many - legs or arms or tentacles or something clinging to my body. I screamed out, Brown says, like a beast, and fell away backward from the step on which I stood, and the creature slipped downwards, I suppose, on to that same step."
A cold face pressed against yours, with arms or tentacles or something clinging to your body - in a sentence or two he out-Lovecrafts Lovecraft and he does it with almost effortless ease.
A third approach is the bare-bones Just the Facts, Dammit! Approach, of which Zelazny was a great exponent. Zelazny's heroes are usually hard-bitten tough-guys (not like MR James' namby-pamby professors of theology from Cambridge) and they describe monsters without fear or emotion:
"There was something unusual about their appearance... For one thing, all had uniformly bloodshot eyes. Very, very bloodshot eyes. With them, though, the condition seemed normal. For another, all had an extra joint to each finger and thumb, and sharp, forward-curving spurs on the backs of their hands. All of them had prominent jaws (and) forty-four teeth, most of them longer than human teeth, and several looking to be much sharper. Their flesh was grayish and hard and shiny. There were undoubtedly other differences also, but those were sufficient to prove a point of some sort." (Fiona's shadow creatures)
"It looked like something that had started out to be a man but had never quite made it. It had been stepped on, twisted, had holes poked into the sickly dough of its head-bulge. Bones showed through the transparent flesh of its torso and its short legs were as thick as trees, terminating in disk-shaped pads from which dozens of long toes hung like roots or worms. Its arms were longer than its entire body. It was a crushed slug, a thing that had been frozen and thawed before it was fully baked."(The Borshin)
"It was well over six feet in height, with great branches of antlers growing out of its forehead. Nude, its flesh was a uniform ash-gray in color. It appeared to be sexless, and it had gray, leathery wings extending far out behind it." (Strygalldwir)
Finally, there is the Poetic Approach, which is the one Tolkien favoured. For Tolkien, evil means darkness, hunger, hatred, and above all self-destruction, and he tries to make this clear in his monster descriptions. Here's Ungoliant:
"[S]he had disowned her Master, desiring to be mistress of her own lust, taking all things to herself to feed her emptiness; and she fled to the south, escaping the assaults of the Valar and the hunters of Oromë, for their vigilance had ever been to the north, and the south was long unheeded. Thence she had crept towards the light of the Blessed Realm; for she hungered for light and hated it...In a ravine she lived, and took shape as a spider of monstrous form, weaving her black webs in a cleft of the mountains. There she sucked up all light that she could find, and spun it forth again in dark nets of strangling gloom, until no light more could come to her abode; and she was famished."
This occasionally gets Tolkien into difficulties, because he liked metaphors and nerds don't always understand metaphor, which is the root of of all those problems about balrogs and their non-existent wings. This hints at a deep problem with the Poetic Approach, which may explain why fantasy bestiaries in particular never use it.
[This post was largely inspired by one of Brendan's G+ posts.]