What different character traits does Victor exhibit at the end in contrast to how he is at the start of the novel?Frankenstein by Mary Shelley

As Frankenstein is a frame story, the end is the beginning, and the middle is a flashback.

So, at the end (or the beginning), Victor is half-delirious and mad (crazy).  Later, once he unfolds his tale, Walton learns that his guest is good-natured and sad.  Then, Victor becomes inquisitive and obsessed about knowing what Walton has seen regarding the Monster.

In telling his flashback, Victor has learned a few lessons in humility taught to him by his creation, the Monster.  Victor has learned to curb his unadulterated passion, his curiosity, his reckless pursuit of knowledge, and his hubris (pride)--all of which isolate him from his friends, family, and community.  All these lessons he wants to tell Robert Walton to convince him from pursuing his romantic dream, the passage to the North Pole, which may cost him many lives.

Still, Victor is hell-bent on revenge.  He is obsessed with killing his monster and, it seems, himself in the process.  He wants to punish his creation and himself for all the lives they, together, have killed in the process.