He must have used the costumes to make real monsters, which implies....

Let's find a way to shut down this monster-maker for good.

Scooby-Doo, raise your right paw. No, your right paw. Your other paw.

The Tar Monster scared the locals of Byzantius away to take their treasure.

Bring it back to the Monster Hive and plug it into the base.

Here we are, folks, on the red carpet at the grand opening...

...of the Coolsonian Criminology Museum.

Tonight's premiere exhibit is a rousing look back...

...at the exploits of Mystery lncorporated.

And here they are.

Folks, this crowd is going crazy over Mystery Inc.

-Fred! -Fred, we love you!

Here you go, girls. I got an ascot for each of you.

Hello!

Check it out! lt's a Shag and Scoob quake and the whole city's shaking!

Yeah!

Come on, Scoob.

Oh, sorry.

I consider it a privilege, sir.

- Daphne! - Don't you two look beautiful. Thank you.