Once again changing the question, since I very very seldom write slash or non-canon pairing and when I do, it's always a pairing I like and I'm able to write. So, that doesn't make for a very interesting answer.
I've mentioned it before, but I tried to write Cas POV once and just failed spectacularly. I like Cas just fine, but I have a specific headcanon for what the inside of his head looks like and I just couldn't capture it accurately, in my opinion. So, that was a little disappointing.
As for characters that I didn't like but found I could write - Draco. I was actually pretty terrified of writing him into the demented'verse, but then once I did, I found that I actually really loved writing him. It helps, I think, that I'm writing him post-series and with an extremely opimistic headcanon for who he becomes.
Similarly, I was nervous about Ron, but I think I did an okay job with him - though, putting him in fics still intimidates me for some reason, so he's been a bit light the last few demented'verse stories. I should probably try to change that down the road.
I'm not sure what's meant by genre here. I mean, I tend to just match the "genre" of whatever show I'm writing about. And I don't write that many shows, so they're all sort of drama with comedy mixed in. Is that a genre? Optimistic amusing drama stories? I guess I tend to go for emotional angst when I write a lot, if that could be considered a genre. I'm fairly fascinated with internal emotional landscapes, so that probably comes through somehow in my writing.
Nope. I don't actually enjoy those all that much... probably because I know exactly where the story is going and therefore the fic comes off as boring. I'm sure there's exceptions to that out there, but I can't think of any off the top of my head.
13 – Do you prefer canon or fanon when you write? Has writing fanfic for a fandom changed the way you see some or even all of the original source material?
I think it's quite obvious that I prefer canon. I actually experience more creative inspiration when given a hard set of rules that I have to work around in order to create a story. It's like... if you give me a box of crayons with every single colour you can think of and ask me to draw a picture, I'll probably sit there forever staring at the blank page with absolutely no idea what to do. But, if you give me only three or four colours and tell me I can only use those, I'll figure something out pretty quick.
As for fanfic changing the way I see some or even all of the original source material? Well... I think that what I said above actually illustrates the change in how I see source material since writing fanfic...
It's gone from "This is a show, be entertained!" to "These are your tools and these are your guidelines, create!"
Which, in my opinion, is pretty damn awesome.