One of the great abilities of Dickens as a writer is the way that he is able to mix horror and ironic comedy together in his work, and this can certainly be seen to be in operation in this great seasonal classic. You will want to consider how the presentation of the ghosts is juxtaposed with humorous commentary concerning the character of Scrooge and how he typically acts. Let us take an example to see this in play. When the Ghost of Christmas Past appears, for example, it is with typical nonchalance or selfishness that Scrooge first asks to cover up the Ghost so that he could see the Spirit "in his cap," then, when he asks the Ghost why he is there, and receives the response "Your welfare," responds ironically to the Ghost:
Scrooge expressed himself much obliged, but could not help thinking that a night of unbroken rest would have been more conducive to that end.
The idea of Scrooge taking issue with the horrible ghost shows something of his hard-bitten defiance and selfishness, which interlaces humour with horror in a particularly Dickensian way.