Events portrayed are biased on the terms of self-interest, specifically moral validation on his actions.
An unreliable narrator leads readers to second-guessing the truth of the novel, and double-checking all the facts of the novel, rather than trusting the narrator’s story.
He had a shift from reliable to unreliable on the very moment that he had completed his experiment -> he was objective, even obsessively objective, as he described in detail what he was doing and why, which as a man of science of that time, it fits perfectly with the character and adds a lot to him being credible and to an extent, pure but -> experiment happens, he starts thinking of his flaws, his errors, his moral dilemmas and he doesn't quite tell the truth.
Story continues with both his point of view and the point of view of his creation, and when they interact, both have different versions of what happened and try to make sense of why.
It is clear that both have the bias of self-interest => both become unreliable narrators.
When Victor compares his feelings to those of Justine, condemned to be executed, and assures us that the 'tortures of the accused did not equal mine' (p. 86), he is a little too self-absorbed to be the best interpreter of other people's feelings -> also despite the fact he knows who the true culprit is.