His limbs were in proportion, and I had selected his fatures as beautiful. Beautiful!--Great god! His yellow skin scarcely covered the work of muscles and arteries beneath; his hair was of a lustrous black, and flowing, his teeth of a pearly whiteness; but these luxuriances only formed a more horrid contrast with his watery eyes, that seemed almost of the same colour as the dun white sockets in which they were set, his shrivelled complexion and straight black lips.
Gothic horror is conveyed in this description as the contrast of what was once beautiful merges with the grotesque: the creature has been formed from beauty, but it is dead, lifeless beauty. The eyes are watery and lacking any sparkle, the mouth straight with no rosy, bloodlife in them. As Frankenstein states, he has tried to "fuse life into an inanimate body," and the result is this incongruity of the creature.
Frankenstein likens him to a demonical corpse to which I had so miserably given life":
Oh! no mortal could support the horror of that countenance. A mummy again endued with animation could not be so hideous as that wretch. I had gazed on him while unfinished; he was ugly then; but when those muscles and joints were rendered capable of motion, it became a thing such as even Dante could not have conceived.
Even after he flees the monster, Victor Frankenstein is haunted by sensations and visions of it:
I felt my flesh tingle with excess of sensitiveness, and my pulse beat rapidly.
Victor is in a state of nervous fever, and refers to himself as in "disorder" trembling with shivers and dread to behold the "monster":
I threw the door forcibly open, as children are accustomed to do when they expect a spectre to stand in waiting for them on the other side, but nothing appeared.
Certainly, Mary Shelley's diction, punctuation, and descriptive passages all lend to the horror of the passages in Chapter 5 of Frankenstein.
To me, the author creates a sense of horror with the events of the chapter, the setting, and the words that she chooses to use.
The main event at the beginning of the chapter is the shock that Victor feels upon seeing the creature brought to life. Shelley shows this with the terrible dream that Victor recounts. I think that the dream really creates a sense of horror.
I think that the setting also creates a sense of horror because of how gloomy it is. The rain, and the fact that it is night combine to make a setting in which you can really sense that something bad will happen.
Finally, the author uses words that make a sense of horror. She talks about the "dull yellow eye" of the creature and about how its movements are "convulsive." The words that she uses in the second paragraph to describe the creature also create a sense of horror.