This is always a fun theme, because it forces us to think about our opinions on good and evil. Neil Gaiman does an excellent job of this in The Graveyard Book. First of all, many of the good guys are supernatural creatures that usually have reputations for bad behavior (like werewolves, mummies, and vampires). On the other side, the bad guys – from the Jacks of All Trades to Maureen Quilling, the ten-year-old bully – are totally human. Some creatures are all good (like werewolves, a.k.a. Hounds of God). Others are all bad (like the seriously disgusting ghouls). But most characters have a choice to make: they can either be good or evil, depending on their actions.
There’s no chance the Jacks could ever become good.
Bod could easily slip over to the dark side if he isn’t careful with his mean streak.