Here are some of the ways I believe Victor Frankenstein fits the typical representation of a narcissist:
Have an inflated sense of self-importance: Frankenstein is a smart scientist, no doubt about it. He creates a living being based on his scientific understanding. Yet he's not humble about his abilities and accomplishments. Check out his rather prideful summary of academic accomplishments:
As I applied so closely, it may be easily conceived that my progress was rapid. My ardour was indeed the astonishment of the students, and my proficiency that of the masters. Professor Krempe often asked me, with a sly smile, how Cornelius Agrippa went on, whilst M. Waldman expressed the most heartfelt exultation in my progress. Two years passed in this manner, during which I paid no visit to Geneva, but was engaged, heart and soul, in the pursuit of some discoveries which I hoped to make.
Frankenstein relishes the praise of his professors and wants his audience to know that it must be obvious that his "progress was rapid."
Are preoccupied with thoughts of success and brilliance: Victor Frankenstein gives up his family in quest of scientific excellence prior to creating the monster. He also notes that "in a scientific pursuit there is continual food for discovery and wonder." Thus, Victor has plenty of untapped scientific "food" to propel his desires for further success and keeps pushing the boundaries of science as he, or anyone, knows them to exist.
Look down on people they perceive as inferior: Frankenstein considers the monster a grotesque being (although it was created by his own hands) and refuses to give this creature any guidance or compassion. Instead of teaching his creation how to navigate a complex human world, Frankenstein isolates the creature based primarily on his hideous appearance. It's interesting that he was seemingly blind to the monster's true appearance until he proved his scientific capabilities. This solidifies his tendencies to be preoccupied with success, and disregard the ways his actions impact others.
React with rage when pressed into a corner: When Frankenstein changes his mind about creating the female companion the monster has demanded, he doesn't simply cease his work. He actually tears the female to pieces as the monster watches, which likely isn't the best move for a peaceful resolution to their conflict over this issue. His rage is reflected in his description that he was "trembling with passion" as he reacted in anger.
Have secret feelings of shame: Frankenstein tells no one about his creation. He tells no one that Justine didn't actually murder William. He warns no one that they could be in danger as the monster seeks revenge on him. Instead, Frankenstein locks away his shame and puts everyone he cares about in harm's way in order to avoid reality.