OK, I actually remembered a case where the additional character not only ruined future episodes, but I retroactively went back and N =now I hate the entire series.
On Bones, brennan’s “lovable rogue” father. Somehow, the creators of a showe about a crimefighter thougt it would be good to have her cover up her father’s crimes (which IIRC included murder, but I’ve purged the whole show from my memory) and have everyone think the was a good thing! Even if he wasn’t a murderer (which I’m. not convinced, despite the trial), he’s still a crook, and I had had enough of the lot by then.
And this doesn’t include Billy Gibbons as Ms Montenegro’s father, or the assassination of Zack’s character. And I quit before the actual “let’s add a baby! that worked so well in every other show that did it” baby arrived. Man this show pisses me off!