Casey Kasem was the voice of Alexander. Since Casey Kasem also voiced Shaggy, the crossover to The New Scooby-Doo Movies resulted in a lot of Talking to Himself. That was particularly weird since, although Kasem is perfectly capable of doing a wide range of voices, he had voiced Shaggy and Alexander pretty much the same way.
The Pussycats were originally meant to appear as teammates of the Scooby Doobies on Laff-A-Lympics, but clearance issues with Archie Comics' imprint Radio Comics prevented it. They were replaced with Captain Caveman and the Teen Angels.