Final answer:
The phrase "Up from his swampland, sliding silently" uses imagery, particularly personification and alliteration, to create a vivid picture and suggest a stealthy movement.
Step-by-step explanation:
The device being used in the phrase "Up from his swampland, sliding silently" is a form of imagery, more specifically, it's an example of personification combined with alliteration. Imagery is a literary device that appeals to the senses and paints a picture in the reader's mind. Personification is given to the phrase through the implied agent sliding 'silently', which attributes human-like stealth or purpose to the subject that is moving. Alliteration is present in the repetition of the 's' sound in 'swampland' and 'silently', creating a smoother sound and emphasizing the silent movement.