Mary Shelley used the device in Victor’s narrative, his monster’s phrases and actions, and nature descriptions. Without any doubt, it keeps readers interested and encourages them to guess possible endings. It is evident that Frankenstein is not a story with a happy end, but full of horror and suffering.
Detailed answer:
First, no wonder Victor’s narrative is full of foreshadowing, as the man shares his story. He says, “Thus spoke my prophetic soul, as, torn by remorse, horror, and despair, I beheld those I loved spend vain sorrow upon graves.” What is more, Victor uses such words as ‘fate,’ ‘omen,’ and ‘destiny’ numerous times. They predict that some horrible events will happen, and some characters will suffer or even die soon.
Second, Frankenstein’s creature behaves and talks in a way, which reveals his monstrous nature. Readers may easily guess that he has no bright future. In contrast, the monster is likely to cause much sorrow and pain. He says, “I declared everlasting war against the species, and more than all, against him who had formed me and sent me forth to this insupportable misery.” He intends to take revenge on his creator, and it can lead only to adverse results.
Third, nature sets the gloomy mood in Mary Shelly’s Frankenstein. The weather is harsh and awful; the sky is grey; the sea is wild. It keeps readers in suspense and makes the novel a real horror. Positive events are unlikely to happen in such a setting. Thus, readers may make pessimistic predictions on the possible endings.