A world in which there are monsters, and ghosts, and things that want to steal your heart is a world in which there are angels, and dreams and a world in which there is hope.
The grammatical structure: Objects and Complements
This sentence consists of a Subject, a Predicator (in other words, a verb) and a Predicative Complement.
Many verbs take Objects, but the verb BE can't. It usually takes a Predicative Complement. A Predicative Complement is slightly different from an Object. Usually an Object talks about a new thing in the sentence. A Subject usually does something to that Object (notice the word usually!). So in the sentence Bob punched the teacher, the phrase the teacher is the Object. It tells us about a new person in the sentence, the person who is receiving the punching action.
But in the sentence Bob is a teacher, the phrase a teacher doesn't tell us about a new person. It just describes Bob. This sentence only talks about one person. And Bob isn't doing anything to a teacher. The teachers is Bob! A teacher is a Predicative Complement, not an Object.
We can break the sentence up the Original Poster's sentence like this:
- Subject: A world in which there are monsters, and ghosts, and things that want to steal your heart
- Predicator: is
- Predicative Complement: [a world in which there are angels and dreams] and [a world in which there is hope]
You will notice that the Pedicative Complement has two phrases in brackets, [ ]. These are joined together by the word and. The phrases in this sentence are very long. So maybe it will help if we look at another sentence with the same structure. Let's look at another sentence with Bob:
- Bob was a singer and a boxer.
We can show this as:
- Subject: Bob
- Predicator: was
- Predicative Complement: [a singer] and [a boxer]
Here, the Subject is Bob. The Predicator is was. The Predicative Complement is [a singer] and [a boxer]. The Predicative Complement has two noun phrases joined by and. Notice these phrases are equal. This sentence means exactly the same as:
- Bob was a boxer and a singer.
Here we changed round the noun phrases a boxer and a singer, but the sentence means exactly the same thing. When we have two equal phrases joined by and like this, it is called a co-ordination. Notice that, together, these phrases do one job. Together they do the job of Predicative Complement. They have one grammatical function. In modern grammar, we could say that the Predicative Complement is a co-ordination of noun phrases. This sentence is exactly like the Original Poster's.
An appositive phrase?
Notice that and a singer is not an appositive phrase. The phrase and a singer does not explain who or what a boxer refers to. We cannot use words like and with appositive phrases. The Original Poster is correct here. An appositive phrase is something like:
- My uncle, a lawyer, is visiting us.
Notice that if we use the word and the sentence will be ungrammatical, or it will mean something different:
- *My uncle, and a lawyer is visiting us. (ungrammatical).
Just like this sentence, the Original example by Neil Gaiman does not include an appositive phrase.
Back to the original example. The Gaiman example has a similar structure to Bob is a singer and a boxer. They both have a noun phrase as a Subject and a co-ordination of noun phrases as a Predicative Complement. Let us call the noun phrase which is the Subject "[S1]". We can call the noun phrases in the Predicative Complement [PC1] and [PC2]. Each noun phrase, S1, PC1 and PC2, has a head noun world. Each head noun is modified by a relative clause. It is the relative clause which makes the noun phrases different from each other. The original relative clauses begin in which and this gives them a certain kind of literary effect. I will replace the relative clauses with with-phrases. I think this might be easier to understand:
- [S1] [A world with monsters and ghosts and things that want to steal your heart]
- [PC1][a world with angels and dreams]
- [PC2] [a world with hope].
Whether or not a writer wishes to use commas in this sentence is a personal choice for that writer. However, notice that PC1 has a co-ordination inside the relative clause. PC1 ends with the phrase angels and dreams. This "and" co-ordinates the two noun phrases angels / dreams. However, right after PC1 we have another "and" that co-ordinates PC1 / PC2. It is helpful to use a comma after dreams here because it helps to show the break between PC1 and PC2. If we don't use a comma, the reader might misread the sentence and think that PC2 is inside PC1. They might think that PC1 has a co-ordination of three noun phrases:
- *PC1: a world with [angels] and [dreams] and [a world with hope]. (wrong)
Of course they will probably realise afterwards that this cannot be the correct reading. But, in general, it is good to make your writing easy for your readers to understand. It might be better, therefore, to include a comma after angels and dreams to separate this from PC2:
- [a world in which there are angels and dreams], and [a world in which there is hope]
Does the Subject contain a parenthetical?
The subject, S1, is a long noun phrase with a relative clause. The relative clause includes a co-ordination of three smaller noun phrases:
- [monsters], and [ghosts], and [things that want to steal your heart]
The original sentence uses commas after the first two nouns. This is why the Original Poster is wondering if and ghosts is parenthetical. The answer is, almost definitely not! The reason is that the writer is trying to make it sound like there are lots of bad things in this world. If the and ghosts was parenthetical here, then this would have the opposite effect, making the ghosts less important.
In addition, the writer is using some well known rhetorical devices to achieve a certain style. These wouldn't work if and ghosts was parenthetical. First of all he is using a list of three things. Lists of three are very effective for giving a sense of drama. Secondly the list gets more dramatic as it goes on. Lastly the writer uses two short nouns for the beginning of the list and then a very long one for the last noun phrase. This well-known device also heightens the sense of drama. If the phrase and ghosts was parenthetical, it would destroy these effects.
Apart from the author's use of commas, there is no reason to think that and ghosts is parenthetical here, because it has the same kind of theme as the phrases before and after it. It's not impossible that it's parenthetical, but it's very unlikely.
I hope this is helpful!