And at this point is where I drop the illustrations - partly to help speed up this group's launch, partly because this last wave of questions is different to those before. They're all meta questions about you and your headcanon, not the world of Equestria. So there isn't much to do except ask, and see how you answer.

My canon hierarchy, based entirely on availability and personal preference:

• The episodes that air on TV are the unmistakeable standard of canon (American version where others conflict). For the most part that also makes them the foundations of my headcanon - but there are elements I miss or mistake, others I forget ( I generally only watch an episode once), and some which I choose to ignore because they're headcanon-incompatible or just plain badly written IMO. I do still have a policy that anything in an episode that doesn't fit the above criteria is true*, but sometimes (thankfully not often) that doesn't leave much of the episode as aired.

  *Songs, background visuals and human expressions are all doubtful.

EDIT: This was written before Season 9 - I decided as soon as I saw the Princesses retiring I would switch to default exclusion with cherry-picking if it was true, and it was, so I did.

• The only other media I pay serious attention too is the books, albiet more at the concept level than the detail one - for the most part, events which could have the same back cover blurb took place in my headcanon. I do draw out interesting elements too, particularly from the older ones, like Cadence's backstory and Aquastria (which I still prefer to Seaquestria even though I've seen the movie but never read the book)!
• The comics are, to me, official fanfiction - no, a whole coordinated official fan verse. Theoretically I reserve the right to mine them for ideas, but in practice that's rather unlikely, especially since I haven't read any of them nor plan too. So you should probably set any ideas garnered from them aside when dealing with me or my work.
• As for anything more obscure, like the card or video game, I'm unlikely to come across it in it's indivdual context but might incorparate some amusing detail if I see it online or something.
• Last but not least, Equestria Girls. Anything episode-length or longer is full canon, shorts are maybe if they stick in my head and don't confuse the timeline too much, comics are as above and this time books are lumped in with them. The whole thing is also on a switch (see next question) so I can turn it off for say, first contact stories.

42. Do you consider official sources other than the show (comics, card game text, movies, novels, etc.) to be canon?
Generally I only consider the show itself to be hard canon. Other official sources I consider to be "soft canon" - that is subject to being overruled at anytime by DHX.

Post-2014 addendum: Given that Hasbro/DHX did in fact overrule the secondary sources a number of times, I stand by this one.

7038836
Given this, do you care if other writers follow or ignore them?

I always put the show at the top and everything else "canon until contradicted by the show". We've had numerous instances where comics, books, etc. became non-canon after an episode aired, but otherwise, they're great for backstories and names of background characters, not to mention original creations like monsters that never show up in the show.

7038969
You don't need to canonise them to raid them, though, any more than other fanfics.

The comics have always been "Secondary Canon" meaning they're canon unless contradicted by the show. It's a shame that that excludes most of their earlier works, because that was arguably when IDW was at their creative best, filling in the gaps and doing things the show either couldn't or wouldn't do. Whereas by marching lock and step with the show, they ended up having to discard most of their greatest works and big ideas.

And I'm gonna have to assume all of the Ponyville Mysteries chapter books are canon, at least to the extent of Scootaloo's aunts since they appeared in the show.

7038964
If a writer wants to adhere to something that was established in the comics or elsewhere that's fine. I certainly don't expect any writer to adhere to something that was established solely in the secondary materials. Especially since it can be cost-prohibitive for most people to follow all of them.

What I consider canon is that which fits to the vision of Lauren Faust. M.A. Larson has done a good job of keeping Faust's vision alive despite the mandates from the devil himself Hasbro, but sometimes I have to take those as a metaphorical representation of what should have happened. For example all the singing in “The Day We Exploded Twilight” was a metaphor for: lifetimes passed, shit happened, Twilight ascended.

7039539
Faust wasn't all hot stuff - there are a few well known occasions where Hasbro meddled her ideas into something better.

And Larson haan't worked on the show in a while.

7039556
I wasn't aware. What things were Hasbro's doing?

7039688
Reducing certain racist implications (the Diamond Dogs were originally stereotypical "Diamond Dawgs"), having Applejack buck trees instead of headbutting them, and probably more stuff we'll find out now that we have access to all the show's development data.

Short answer: No.
Long answer: Only if I like them, which is, frankly, not often. I already tend to toss out much of the later seasons of the show. I'd say the largest secondary source I accept is Rainbow Rocks (and EQG by extension since it's a sequel to it). Otherwise, the comics I by-and-large discard out of hand (look how they massacred my girl) and things like card text are very inconsequential, and in general, take-it-or-leave-it.

7039889
Your girl?

And where do you start tossing the show?

7039892
Chrysalis, generally portrayed in the comics as straight up a two dimensional classic Disney villain.
I started getting leery right about the Season 5 finale, but To Where and Back Again was the last straw. They really shouldn't have waited for Larson to leave to do another changeling plot.

7039895
Just because you like her with more depth, doesn't make her being just villain wrong. She certainly didn't show any more depth in Canterlot Wedding.

7039928
Oh, but she did. Note that in A Canterlot Wedding her goals were focused on the changelings as a whole, rather than a selfish 'mine, mine, mine!'

7040007
Debatable. Sure, with plenty of love to go around she's happy to let her followers take her share as long as the prime prize is all hers.But neither said lesser changelings nor her relationship with them is dwelt on. Leaving room for several interpretations.

I could probably phrase it a little bit more diplomatically, but quite honestly: I never bothered with any 'other material'. (Comics, books, card texts, whatever else there might be.) I watched the show. I watched the movie. I watched the Equestria Girls stuff. (Actually excluding those... how long were they? Those three minute shorts?) I'm on the fence about Equestria Girls. I accept most of the show as canon, though let's be fair here - the show contradicts itself in more than enough places to make wrangling a coherent 'canon' from it a funny business already.

Maybe I would allow books and other media into the canon if I would ever bother reading them. Because at the end of the day, their viability really depends on the quality of the material and possible contradictions. Though I agree that something doesn't have to be canon to serve as an inspiration.

All that being said, my head-canon has some significant deviations from the storyline presented in the show anyway. My changelings never reformed, for example. I know that many dislike their new design. I don't. I dislike their new role. It's bland. The black carapaced predators have a way more interesting dynamic. And there's more than one hive, subsequently ruled by more than one queen. (Chrysalis lost most of her hive in the Canterlot attack. She's currently trying to dispose of another queen to take over her hive for a second attempt.)

In my version, there's a Friendship Castle - but no School of Friendship. I know that this makes it seem like I'm disregarding a lot about the later seasons, and in a way, I guess I am. Again, though: Not out of a dislike for the content. (Though that last episode doesn't exist, as far as I'm concerned.)

The heaviest change is probably this one: My version doesn't have Discord. He exists. He was frozen in stone. He escaped... and was blasted and disembodied by Celestia in secret, because she felt Twilight wasn't ready to face such an almost omnipotent nightmare as him. She hopes that his time as a powerless, observing spirit might help him cool down and disregard his need for vengeance until his body reforms and they can maybe attempt to make up in peace. She doesn't know that he's a funny guy and kinda lives in Pinkie's mane now, as a sort of roommate. Discord's absence obviously has some implications for other events, but I mostly try to find explanations to keep them close to what happened in the show.