How has he moved so quickly from childlike naïvité to existential panic?

It is true, we shall be monsters, cut off from all the world; but on that account we shall be more attached to one another.

It’s no use going back to yesterday, because I was a different person then.

Accursed creator! Why did you form a monster so hideous that even you turned from me in disgust?

How did he get so terribly smart, so determined? Maybe it was the pain I'd caused that made him that way, and if that were true, then I'd sort of had a hand in it, in making him as smart and devious as he was. I was really starting to dislike the guy. But I also felt a little proud, like Dr. Frankenstein must have felt when his monster turned on him, because after all, it was Dr. Frankenstein who had made the monster strong and cunning enough to turn on him.

My reign is not yet over... you live, and my power is complete. Follow me; I seek the everlasting ices of the north, where you will feel the misery of cold and frost to which I am impassive. You will find near this place, if you follow not too tardily, a dead hare; eat and be refreshed. Come on, my enemy; we have yet to wrestle for our lives; but many hard and miserable hours must you endure until that period shall arrive.