According to Dictionary.com foreshadowing is:an advance sign or warning of what is to come in the future. The author of a mystery novel might use foreshadowing in an early chapter of his book to give readers an in linking of an impending murder.
Foreshadowing is a very common literary device in literature. Mary Shelly's Frankenstein is no exception. The beginning of the book talks a lot about Frankenstein's childhood and how he had such good parents. This could be a foreshadowing to how Frankenstein would in turn take this good childhood for granted and not realized how much work it is to raise a child. This could be foreshadowing how he is not going to be a good father to Pieces.
In the writing of Frankenstein Mary Shelly uses a lot of words such as "omen" and "fate". These could all be instances of foreshadowing in the book. Past tense is used to describe the character of Clerical. This use of past tense might signify the eventual death of the character.