The Scooby-Doo Show

After winning a contest, the whole gang goes on a vacation cruise. On board the ship is a rather nice professor, along with some investors of his who are interested in his time machine. Testing out his time machine, for his investors, the professor unleashes a monster from five thousand years in the future into our modern world. Trapped on the boat, the gang have nothing else to do but return the mean monster to the future.