Honestly, Jim Nightshade leaves us scratching our heads a bit. We'll start with a brief comparison to his buddy Will. Will has white-blond hair, Jim has hair that's "wild, thick and the glossy color of waxed chestnuts" (1.14) (in other words, his hair is dark). Will was born one minute before midnight, Jim was born one minute after. Will is thoughtful, Jim prefers action. We could sit here and play the opposite game all day, but that's for our discussion of foils in "Character Roles."
Between you, us, and the Internet, the reason we scratch our heads over Jim is because the brief glimpses we get of his character are, frankly, kind of freaky. Remember, most of the novel is focused on Will and his thoughts. We get only a few glimpses into Jim's life and head, and what we see is pretty off-putting. Let's examine the evidence, shall we?
Chapter 9 is the only chapter in the novel that focuses purely on Jim. In the chapter, his mother tucks him into bed and expresses the desire that Jim one day have plenty of children. Jim's response? "No use making more people. People die" (9.19). Later in the chapter, Jim decides he wants to see what will happen if he takes down the lightning rod protecting his house: "Why, he thought, why don't I climb up, knock that lightning rod loose, throw it away?" (9.43). If we read this chapter in isolation, we'd assume Jim has some kind of morbid death wish. Then there's his activity as a Peeping Tom, which is part of his broader desire to grow up, stat. To this end, even when the carnival is demonstrably E-V-I-L, Jim still heads straight to that magical carousel every chance he gets.
So for us, there are a couple major questions around Jim and his character. If Will and Jim are such opposites, and Will is "all good" (28.6), does that make Jim all evil? Why are Will and Jim friends in the first place? Will they continue being friends in the future or are these differences just too fundamental?
To add one more ominous dimension to Jim's character, we advise you to check out Chapter 9 in greater detail. In particular, note that Jim's mother bears a face "that had been hit a long time ago. The bruises had never gone from around her eyes" (9.31) and also that Jim once had two other siblings. It is implied that Jim's father was abusive to his mother, which means that part of Jim's "darkness" comes from his family – fitting, since it is reflected in his family (last) name, Nightshade. This raises some interesting questions as to how responsible Jim is for his darker nature, or even how responsible any character is for his natural inclinations. If it's a matter of the family you're born into, or even the time of day you were born, is there really anything you can do about where you lie on the good vs. evil scale? Another Big Question, courtesy of Mr. Bradbury.