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The Crossword Puzzle Ghost was the disguise of an unnamed villain.
He was a nearly-bald male in a cloak with a huge, possibly fake, tooth.
He is obsessed with puzzles, enough to construct a crossword puzzle for the gang to solve that gave away a major secret of his.
Skills and abilities
He was skillful in making crossword puzzles and trap doors.
Scooby-Doo! (DC Comics)
The gang solved his crossword, which identified which book opened the secret door to his hiding place. Then they switched the book to a different place to trick him into trapping himself.
Crossword Puzzle Ghost: Before you try to open the secret door, I must warn you that only one book is the key to open it. It will take cross words to find it.