The Castle of Otranto by Horace Walpole uses several literary devices to create his tale of horror and suspense.
The author uses sensory details (details that appeal to the senses) to create the mood of this dark tale. In the following excerpt, the temperature of Isabella's hand clarifies in the reader's mind not only her unstable emotional condition, but also draws a comparison to death, something with which cold is closely associated:
At those words he seized the cold hand of Isabella, who was half dead with fright and horror.
The following example uses personification.
...he saw [the portrait] quit its panel, and descend on the floor with a grave and melancholy air.
Personification is a literary device that gives human characteristics to non-human things. "Air" is used to refer to attitude or mood, which a painting (not the subject of it) cannot have.
Another example of personification is:
An awful silence reigned throughout those subterraneous regions...
A king reigns over people under his power. However, silence is not human but a thing, and cannot reign. This is a use of figurative language, not to be taken literally.
The literary device diction effectively applies "word choice to create a specific effect." Details that create a sense of darkness and doom are found in the words "grave" and "melancholy." Diction is of particular importance in sustaining the mood, once it has been established:
...[her father's] obscure menace to the Princess his wife, accompanied by the most furious behaviour, had filled her gentle mind with terror and alarm.
The words that create a sense of foreboding are menace, furious, terror, and alarm.
Imagery creates a vivid picture in the reader's mind. Nearly hysterical, Jaquez says...
…we heard a violent motion and the rattling of armour, as if the giant was rising...
The author uses onomatopoeia to advance the fearful mood of his tale. "Rattling" is a word that often brings to mind the image of bones shaking, the hollow sound they make—or even, as is the case here, the hollowness that would be heard in empty armor. And if the armor is also moving, this promotes a sense of fright as well.
Using ominous words, imagery, sensory details, and personification, and even onomatopoeia, the author creates a dark and frightening mood of terror in this story of the earliest origins, a predecessor to other classic tales of horror such as Shelley's Frankenstein and Edgar Allen Poe's "The Telltale Heart" and "The Black Cat."