Twilight X Harry Potter Bleefic - Bella Marie Potter Cullen: The Girl Who Lived - I can't find the original copy of the fic, so I hope the sporking by Zelda Queen from Das Sporking will suffice for your entertainment, even if it means we probably can't mission it . Seriously, doesn't that title alone make you cringe? It was practically impossible for this thing to have been anything other than an absolute train-wreck from the very beginning!
Because - Sailor Moon - I'm more confused than anything else about this songfic. If this wasn't a songfic or if the author had chosen a different song, it might have been decent. At it stands, on one hand we have a cute hurt/comfort story about Serena and Rini comforting each other after Darien gets hurt. But on the other hand, the meaning of the lyrics of the song Because of You, by Kelly Clarkson, completely contradict the dialogue that precedes them, which copy them almost word for word but still gets the meaning wrong.
Fics that I'm unsure of how to feel about.
Arthur goes Fourth and Arthur goes Fifth Series - Rated K+, but you could probably argue that rating is far too low
Introduces uncanonical and dark elements like Aids, drugs and war. Also introduces other uncanonical but more silly elements like time travel and unicorns. I will leave it up to you to judge wheter the writing is good enough to excuse this or not.
Respect - Puella Magi Madoka Magical X Smile Pretty Cure - Rated T - Darkfic, Horror, contains extreme violence, angst and disturbing imagery.
If this was a standalone Madoka darkfic, it would be pretty par of the course. A story about a budding artist getting brutally bullied because of her "childish" interesting, who then made a contract with Kyubey, making a wish that people would respect her drawing, which then resulted in her getting a sketchbook capable of trapping and killing people, would be the sort of thing that would pretty much expect from the Madoka fandom.
But as you may have noticed, this is a crossover with Smile Pretty Cure and the character in question is Yayoi Kise. Who kills her own mother, the 4 Pretty Cures, Candy and practically the entire town, including the police force. There is also the matter of the cross-canon contamination of Yayoi eventually becoming a Witch, not just any Witch mind you, but especifically, Izabel, the Artist Witch. I'm pretty sure that having a canon from one continuum become a canon from another, entirely unrelated continuum would be... problematic to say the least.