what does the creature decide to do? what is his new plan

The creature curses his creator for giving him life. Only his great rage, and his consuming desire for revenge, keeps him from taking his own life: he longs to "spread havoc and destruction around [him], and then to [sit down] and enjoy the ruin."

He falls upon the ground in utter despair and, at that moment, declares war upon all mankind for its callousness and cruelty. He vows to exact revenge upon his creator ­ the man who "sent [him] forth into this insupportable misery."