The book opened with a pancake shaped creature taking a kid under the covers transporting them to another world. The cover was dark blue with the kid in bed pulling the covers up and the creature at the foot of the bed. It was more fantasy than horror.
Stump the Bookseller
New format, same book stumper solving.
Is this The Grumpus Under the Rug by Ellen Jackson?
Mother doesn’t believe there is a Grumpus under the rug causing all the mischief, even though her little boy keeps telling her so.
https://books.google.ca/books?id=4pwCAAAACAAJ&source=gbs_book_other_versions