The title The 13 Ghosts of Scooby-Doo identifies 13 ghosts.
The 1985 animated series centers on Scooby-Doo, Shaggy, Scrappy-Doo, and their companions as they attempt to recapture thirteen ghosts that were accidentally released from a chest. Each ghost has distinct powers, a separate personality, and a different challenge for the group.
The series is notable because it treats the ghosts as genuinely supernatural rather than revealing every threat to be an ordinary person in disguise. Vincent Van Ghoul assists the group, while Flim-Flam joins the younger characters during their travels.
The number in the title is therefore part of the show’s central premise, not merely a general reference to ghosts. Later Scooby-Doo productions have reused some characters and concepts from the series, but they do not change the original title’s count.