* EarWorm: The theme song, so much that over a decade can go by without hearing it, then one day the show suddenly springs to mind and [=BAM=] there it is again.
* DesignatedVillain: There were episodes where Sylvester didn't do anything to anyone at all, including Tweety, yet he was still mercilessly tortured by sadistic plane gremlins and murderous mice.
* SeasonalRot: The first season made genuine attempts to tell compelling mysteries and stories. While the second and third seasons aren't bad, they are of lesser quality since they barely focused on the mysteries and characters, and were pretty much just regular Sylvester and Tweety cartoons.
* UnintentionallySympathetic: Sylvester in some episodes, as mentioned above. It also didn't help that some episodes had him saving his oblivious owner and her other pets from danger, and never being believed or thanked for it.