A Pup Named Scooby-Doo

Season 1, Episode 2

Episode Title: The Sludge Monster from the Earth's Core

Air Date: 1988-09-17

Overview:

The Coolsville bank is robbed. The janitor says that he saw a monster in the vault but nobody believes him and he is accused of the robbery. He's proven right when Scooby finds the monster inside his doghouse.