The narrator of The Graveyard Book is a third-person omniscient narrator. The narration mainly follows Bod throughout the novel. But we also get information about important other events in which Bod isn’t included directly.
A good example is the interlude. The narrator gives us some information about the Jacks of all Trades. Also we learn something about the man Jack and the situation he is in. This is all information that Bod is not privy to.
Another example is the fight of the Honour Guard against the Jacks in Poland. The narrator switches the setting from Bod and the graveyard to the battle in Krakow.
Furthermore, there is a moment towards the end of the book where Bod fights the Jacks. The narrator switches from Bod’s perspective to Scarlett’s perspective and we learn something about Scarlett’s view of Bod when he kills Jack with the help of the Sleer (“You aren’t a person. People don’t behave like you. You’re as bad as he was. You’re a monster“ (286)).
The effect of all of this is that the narrator is able to provide more information about the characters and the whole story gets more thrilling.