There was one Pokémon badfic I found that was pretty bad. Spelling and grammar that rivaled My Immortal, a blatant Mary Sue named Ruby, reality that remained inconsistent (her love interest died no less than four times), and crossovers with Titanic, Avatar the Last Airbender, Twilight, and even reality. The author would write amusing death threats to various people who wrote bad reviews, and would devote entire chapters to killing them off. Too bad it was a Trollfic. I had so much fun with it that I made it into the (planned) first episode of my own series, Imaginations Collide, if anyone remembers me mentioning it.
Other than that, I'd say it's a toss up between The Girl Who Lived Septology and a Walking Dead badfic I found called The Walking Dead Reprisal.
The Girl Who Lived doesn't have that many spelling mistakes compared to other badfics I have read, but the so called logic of the series is painfully bad. There is one point where the main character teleports to deliver a letter from somewhere where she is trapped, and then goes back to where she is trapped! It would have made much more sense to just teleport out and stay there, right? And then there is the horrendous pro-nature, pro-nudist and arguably pro-gay themes in there. Not that I have a problem with any of those things. I mean, I personally don't conform to those viewpoints. But I'm open-minded enough to tolerate them, as long as they are not forced down my throat, like this set of "stories" does. Of course, the main character is a Mary Sue, and the main characters are put out of character.
But as a side note, this series had so much potential, even though it is a rip off of the Harry Potter series. For example, two of the main characters, Ron Weasley and Neville Longbottom, are taken out of character, sure. But Neville is given a more interesting backstory, and Ron has replaced Ginny in the Chamber of Secrets as the vessel of the diary. These things could easily have worked, and that's what is frustrating! Neville is given a more interesting backstory, but his personality is very much like Ron at that point, and they are used interchangeably, when that should never happen! Ron being the victim of the Chamber of Secrets could have been really good, if he was kept in character and wasn't reduced to a weak and helpless ***wipe.
And to top that off, there were several new aspects of this story that I was looking forward to. The Druids were just begging to be more fully explored! And if they were going to be used, then- The story mentions Necromancers! That would have been awesome!
The reason I hated this series so much is that it had so much potential. I genuinely wanted it to turn out to be something more than it is. Unfortunately, the author just took on something too ambitious for them to handle.
The second pick I have is The Walking Dead Reprisal. This Mary Sue has a Katana and two pet wolves. Yes, a pair of pet wolves that she had met on her travels and tamed to follow her and attack on command! The sword is pushing it, but I would have let it slide. The wolves, on the other hand... Why?! Why a pair of wolves and not something more realistic, like a pair of regular dogs? They're still cute, they could still help her out, but they provide the extra challenge to protect because they were, I don't know, domestic at one point or something and not really used to fighting for their lives! But I'm going off topic, here. There is something set up at the beginning that I'm probably making more out of it than it really is, but it seems that there is some secretive shadow government watching Mary Sue in this story. And guess who Mary Sue falls in love with. DARYL, of course. And she meets him and his group when they are searching for that little girl. She follows them to Hershel's farm and tries to steal from them, but gets caught. I think it was Shane and Andrea who were the ones who were out of character and wanted to get rid of her. Shane probably would have done that in the TV series, but not for the reasons that were given. The series goes on and last I read, the crew was in the prison. I do not like this one because the Mary Sue is a classic case of when a main character, in this case, Daryl, falls in love with the Mary Sue for no real reason and with little to no time at all, when in fact, it's not in his character to do so.
So those are my Dishonorable Mentions. I hope you enjoyed them, they were The Gratest Pokémon Master (yes, that is how it's spelled), The Girl Who Lived Septology, and The Walking Dead Reprisal. And when I say "enjoy", I really mean "develop a brain tumor from pure frustration and vomit out your last meal from disgust". Here are the links.
https://www.fanfiction.net/s/8706167/1/The-gratest-pokemon-master
https://m.fanfiction.net/s/9389565/1/The-Walking-Dead-Reprisal
https://www.dropbox.com/sh/gbmzecr4qtyt1y7/CKTkvQkQQK