When I beta, plot is the most important thing, closely followed by grammar and your story's flow. Of course, in characterness, Mary Sues, and the like are also all put to my attention. I can help with accuracy to canon, though my knowledge fluctuates greatly with each fandom. (see list below)
The main thing I will look at is not your grammar and typos, but the actual writing. Does that sentence flow, is there a better way to phrase this, would they really do that? I will nitpick every single thing that I
I will not sugar coat any problems. If I think something is bad, I will tell you. I do not mind ships, and I will beta any genre. I will only do stories that are in a fandom that I know and enjoy (read very bottom for exceptions), as I do most of my work within the plot. I enjoy both AU's and OC's, along with canon divergence and other variations!
If you want me as your beta, PM me with a description of the story, as well as anything that you think would help me as a beta, and the things that you need to improve on. If your story is something that is not my cup of tea, but you still want me to beta it, we can talk it over through PM. I can be flexible. I miss emails a lot notifying me of messages! If I don't reply after 3 days, message me again! Or hit me up on tumblr!
Fandom knowledge (For specifics, PM me)
Experience with fanfiction:
Very knowledgeable: Hunter x Hunter (Manga and 2011), Naruto (OG and Shippuden), Pokemon (mostly video games, some anime, clueless about manga)
Knowledgeable and up to date with source: Soul Eater (Soul Eater leans more towards MakaxSoul ship as far as knowledge goes; anime and manga), Fullmetal Alchemist and Brotherhood (anime only), Ouran Highschool Host Club, Akatsuki no Yona
Knowledgeable but fell out of reading and need to get around to reading again: Shingeki no Kyojin, Tokyo Ghoul, Kuroshitsuji, Ao no Exorcist
Knowledgeable but not complete (and most likely not finishing): Kuroko no Basuke
I know the series and have read fics, but I'm not really an expert (mixed bag of knowledge): Zelda, Dengeki Daisy (Not complete, can be if needed), Durarara (anime only; none of the recent seasons)
Little/No Fanfiction experience but I know the series from casually watching it (completion of series varies):
Books: Harry Potter, Percy Jackson (only up to House of Hades), Maximum Ride
Games: The Legend of Zelda
Cartoons: Teen Titans, Danny Phantom, Code Lyoko
I know many other fandoms, though my knowledge may be lacking. Again, PM me if you have any questions or if you want to know story preferences.