Victor's dream foreshadows the ultimate destruction of his bride and his stable life. This dream comes on the night he has "beheld the accomplishment of [his] toils". He runs from the room, locks himself in his bedroom, & falls into a fitful sleep. There he dreams:
I thought I saw Elizabeth, in the bloom of health, walking in the streets of Ingolstadt. Delighted and surprised, I embraced her; but as I imprinted the first kiss on her lips, they became livid with the hue of death; her features appeared to change, and I thought that I held the corpse of my dead mother in my arms; a shroud enveloped her form, and I saw the grave-worms crawling in the folds of the flannel.
This also seems to suggest that Victor will cause Elizabeth's death, as evidenced by the fact that his dream kiss causes her to transform into a corpse. The fact that it is the corpse of his mother suggests something else entirely. Note the imagery here: "livid with the hue of death", "shroud enveloped", "grave-worms". This is powerfully descriptive diction that reflects the description of Elizabeth's corpse later in the novel.