It is meant to be from Secret Agent grandma, it even has art that replicates the cover, I'll need to fetch it for proof, but it's specifically used for a screen reminding you to do the event stuff before it ends and that isn't popping up for me. (I mean, even without that bit, this granny arrives to visit a kid and is an alien, which is indeed a part of that book.
It is the best I could think of, but it seems logical because the witches in Goosebumps 2 look ghost-like. As for the flying jack-O'-lanterns, that one feels kind of obvious and straightforward. Those names can do until someone who plays HorrorTown can come up with something else.
As for the Ghostly Witches and Flying Jack-O'-Lanterns, they may be named differently in HorrorTown. If anyone wants to rename those pages, they must first check HorrorTown to see is those monsters have names other than what their pages call them.
I looked into it, and the witches are merely summon able monsters you summon from Fred's Pharmacy so they aren't given proper names. (It just says "the Witches") I think the flying pumpkins only truly appear on that loading screen.
A curious fact is that when i first saw the Captain Long Ben for the first movie, at first i thought it was not him, because in the books, he had more "zombie-like" appearance, but seeing that it was really him, I am quite surprised, since it didn't look anything like the one in the book, so after seeing the second movie and seeting that an Undead Pirate appeared, I thought, "maybe it will be that the pirate that appears in the second movie is the Captain Jack-the-Knife ?"