One example of a "shark" on this classic sitcom was the dumbing down of the Screech character. Originally he was very bright and slightly quirker. As the years went on,he became extremely quirky and very stupid. This is one reason the Tori episodes are nearly unwatchable.
In any case an excellent example of Screech's stupidity is "Screech's Spaghetti Sauce," although I don't think it is just Screech that is stupid.
On the surface this could have been a classic episode. After all, Screech appears to hatch a good scheme (very rare in later years) and even begins dating an attractive girl (another great rarity). Even the exchange where Zack tries to tell Screech that Robin is only dating him for the money, in a better plot, could have been a really awesome scene.
Instead, once again Screech messes up, and is made to look like a total idiot and a complete loser. The other members of the gang are mad at him, and slam him yet again (Jesse, Zack, and Lisa do this constantly as the years go on).
There is something(s?) I don't understand though. Screech and the gang were "busted" for using "Betty Crocker's" (specifically) "recipe" for spaghetti sauce. Someone should fill me in here, but it has been my understanding that it was very difficult (if not in fact impossible) to copyright a specific food here in the USA. This was even addressed in an SBTB episode when one of the teachers (Mr. Tuttle perhaps?) makes a direct reference to "Pepsi and Coke." How would the gang be in violation of copyright by making a sauce with the same ingredients as Betty Crocker? As long as they do not use the words "Betty" or "Crocker" or some logo I see no problem. Oh well, I'm sure I am reading too much into this, in any case, but I remember being frustrated when I first saw this episode as a boy.