Contributed by The Editor.
When Scooby-Doo, Where Are You? first came out, it was firmly established in each episode that the ghosts, monsters, etc. were always fake. But, in subsequent incarnations of the show, the preternatural began to become much more commonplace. Compare the rubber ghosts of Scooby-Doo, Where Are You? with the “actual” ghosts of The Thirteen Ghosts of Scooby-Doo. It appears that adding the “actual” ghosts was another attempt to add new life to the franchise, following the disasterous addition of Scrappy-Doo to the list of characters. It is also worth noting that in A Pup Named Scooby-Doo, all of the monsters are fake. Even though this series was produced after The Thirteen Ghosts of Scooby-Doo, it takes place before it, when the monsters were still people in costumes.
Don’t forget though, there was a real ghost in A Pup Named Scooby Doo. They had one episode taking place on Halloween, where they were hired by a small Droopy-esque ghost named Mr. Boo, who was trying to save his haunt from being destroyed because of a fake ghost pirate.