A Pup Named Scooby-Doo (1988)

S1E4 The Schnook Who Took My Comic Book

At the Coolsville comic book convention, Scooby and Shaggy discover that an old friend has been keeping the rare #1 issue of Commander Cool just for them. However, their excitement turns to panic when one of Commander Cool's foes shows up, intent on snatching the coveted comic away from them.