Some frequent examples of headcanon include relationships between characters, abilities, events following the conclusion of the work, etc. which the author or creator has not explained or included. For example, a consumer may "read between the lines" and assume that there was a previous romantic relationship between two characters where no conclusive evidence actually exists of one. Some fans who come up with particularly interesting or convincing generated headcanons may decide to share them with others in hopes that their idea spreads. Faith and belief are or should be flexible in at least some respects, and there are gaps that need filling, particularly in the case of traditions whose historical practices are missing or have been destroyed. Which, when you think about it, are all kinda the same thing.
What’s more, they are all easily recognizable and their involvement in any story can make it stand out. It’s all fun and games until Arbiter Daos asks to see you. But there is something that should be avoided heavily and that’s integrating an NPC into your character’s story in such a way that they had an active role in your character’s life if not still do. No, I don’t mean metaphorically, I mean everything.
As mentioned, canon is really the only arbiter you have to rely on and, thus, the primary thing roleplayers utilize to ground their characters in reality. There are three ways you can address canon to bring your headcanon into reality. Headcanon is any lore created by someone without authority over a property that explains, alters, or adds to established canon. This can range from fanfiction to fan theories (I see you, MatPat!) and everything in between. Headcanon is just the stuff you read into the world. Like your theory as to why Sherlock and Dr. Who would make an amazing couple.
But you're not sure they're actually doing that, because you don't roleplay. Admittedly I haven't been involved in the roleplaying community on Homecoming, so maybe they don't have that issue here. It sure seemed to be an issue on the retail servers though. ALL the Zig maps show some level of damage, and ingame text makes it clear the place is in a constant state of "under repair from one or more breaches". Which makes perfect sense, considering that supermax or no, it's still an effort to keep superhumans (some of whom are capable of Boomtown-level destruction) locked up with mostly mundane technology. Breaches WILL happen even without outside shenanigans, and they're going to be messy when they do.
Nonetheless, in recent years in entertainment and the arts, there is a rise in good writing for autistic characters. Plus, some shows such as the SHE-RA reboot officialized the autistic headcanon for some of their characters. This a great progression from the subpar representation I had to deal with growing up, and I want to see more of them in media in the near future, hopefully with acceptance and diversity. In other words, all the stories exist, but not all of them "count" for whatever the current story that is being told.
COULD he have tried squishing Kai or Arte like bugs? So it was never tossed on the proverbial table as an option. My headcanon generator is always very self-contained as well. The characters in my Paragon PD SG have met Blue Steel, but he doesn't look up to them or owe my characters any favors.
One popular fan theory is that Draco Malfoy is a werewolf. There are online videos, there are reddit threads, and people have argued back and forth to no end as to whether or not Draco has lycanthropy. The theory gained so much traction, and so many people had accepted it into their headcanons that it got attention from JK Rowling herself… who shot it down. A while back, many of us internet denizens were led to believe that Daryl Dixon could potentially be gay.
And yet, for many people, Draco Malfoy is still considered a werewolf. While JK Rowling has denied the werewolf theory, there are many who reject her view. Indeed, there is a rather large camp of people who claim that she stopped having control over Harry Potter once the seventh book was released.