Despite coming in dead last on our list, the version of the Joker that appeared on The New Scooby-Doo Movies isn't unforgivably terrible—which is unfortunate in a way, because that would at least be fun to talk about. This guy is just flat-out boring, to the point of being functionally indistinguishable from any other weirdo who dressed up as a monster to fake a haunting before ultimately being defeated by a gang of meddling kids. And that might be an even bigger problem.
It's one thing to be taken down by Batman—that's like a supervillain badge of honor—but the Joker and the Penguin remain two of the only bad guys who somehow managed to not scare Scooby-Doo, a character who's literally defined by being afraid of everything. They end up doing the opposite, planning to frighten the gang and ending up enticing Scooby to chase them with the sight of delicious bones. The only way that could've been a worse plan is if they'd dressed up as improbably huge sandwiches.
The devastating failure on display here only cements the bottom-of-the-barrel position that Scooby-Doo's Joker earned. The only thing that's really worth mentioning about him is that he was played by veteran comedian and actor Larry Storch, and let's be real here: that's only really interesting if you're the kind of person who likes to get into some hardcore trivia about the cast of F-Troop.