In the last half of Mary Shelley's "Frankenstein," does the monster become in any way Frankenstein’s double?
In this educator's opinion, the creature or monster does not become Victor Frankenstein's double; he becomes Victor Frankenstein's better. Whereas Victor, by his own description, becomes obsessed with experimentation the morality of which he concedes is highly questionable ("Learn from me, if not by my precepts, at least by my example, how dangerous is the acquirement of knowledge, and how much happier that man is, who believes his native town to be the world, than he who aspires to become greater than his nature will allow."), the creature shows every sign of being shaped entirely by his environment and circumstances. While nothing could excuse the creature's murders of innocent and good people, it is very clear that only its rejection by Victor and others has left it with no alternative but to reject mankind and to strike out at it.
The turning point for the creature, even after its immediate rejection by Victor, is its encounter with the De Lacey family in the woods. The creature's extended period surreptiously observing this family of kind and decent people shapes his character:
"The young girl was occupied in arranging the cottage; but presently she took something out of a drawer, which employed her hands, and presently she sat down beside the old man, who, taking up an instrument, began to play, and to produce sounds, sweeter than the voice of the thrush or the nightingale. It was a lovely sight, even to me, poor wretch! who had never beheld ault beautiful before...I felt sensations of a peculiar and overpowering nature...and I withdrew from the window unable to bear these emotions."
The creature becomes virtually a member of the De Lacey family, albeit without the family's knowledge, collecting firewood for it and planning a future among it. The surprise and violent reaction of Felix, the son and older brother, to the vision of the creature represents an emotional cataclysm from which the creater does not return. Even its demand upon Victor that the latter create a mate for it, following which it will remove itself from society forever, is little solace for the violently and viscerally rejected being.
Victor's repeated cold rejections of every entreaty from the creature leaves one with the distinct impression that the latter was a morally superior creature to the former, but for the inconvenient matter of those deaths.