"Hassle in the Castle"
The gang goes out on a boating expedition, but get lost in a fog and runs aground on Haunted Isle. They decide to venture to the abandoned Vázquez Castle on the island for help, but instead encounter a transparent phantom who scares and warns them to leave the island and never return. The gang tries to capture him but instead they pass through the Phantom and they learn he seems to be able to walk through walls.
This was the first episode to open with the familiar vocal theme, sung by Larry Marks. All subsequent first season episodes open with Marks' version of the theme. This was also the first episode to use the standardized episode title card.