More headcannons because I have not been able to stop thinking about this franchise for the past 13 years, and I have over a decade's worth of opinions.

I've already posted some of these ideas but ehh it's fine.

While I enjoyed watching it for the first time, THW was disappointing to me for a variety of reasons. (The music was probably the best out the franchise though, I'll say that) Grimmel didn't reach his full villain potential since the writers used Ruffnut's lack of judgment as his key to success instead of him being a capable strategist. (Also they did my girl so dirty. She may be a dumbass, but she's not an idiot!) I don't like that the dragons left after just 6 years. I don't like that all the riders except for Hiccup and Astrid are just played for laughs instead of shining like they do in RTTE. I don't like whatever the hell Snotlout's obsession with Valka was, and I didn't like Toothless' "romance" with the Light Fury. I hate that even dragons can't escape half-developed romance and a nuclear family as the ultimate character accomplishment.

So here are my edits (looking back, there's quite a bit going on, so it may need to be split into 2 movies or a short TV series)

The time jump happens between movies 2 and 3. (I want a full movie with bearded Hiccup and "Homecoming" does NOT count) 10-15 years have passed, so the riders are about 30-35. Zephyr and Nuffink are either little kids or preteens and are getting to an age where they're starting to train dragons.

Astrid is more rough around the edges like she was in HTTYD 1 and Rob/Dob/RTTE, not just Hiccup's supportive gf/wife. Instead of making her softer, motherhood has made her fiercer because she has more people to protect. Hiccup on the other hand is a doting father and can't say no to the kids if they give him puppy dog eyes: heart melted every time.

Toothless finds his original flock(?)/herd?/murder?/unkindness?/parliament? of Night Furies instead of just one "soulmate". Each can have their own personalities and roles in the group while Toothless is the baby. I think it would be interesting if, like Hiccup, Toothless was quite small compared to his peers - potentially explaining why he was on his own and got separated from the group before meeting Hiccup.

Dagur and Heather are brought into a council meeting as Berserker allies. Hiccup greets them in a way that clarifies things for audience members who haven't watched the show. I suppose Mala would also be in it too. I don't dislike Mala but I hate her and Dagur's relationship. More development needed there.

Gustav should be there too, still very much trying to prove himself as a dragon rider and occasionally messing things up.

In terms of the main plot and villains, I'm not too picky, although I've said before that I'm tired of dragon mind-control being the main villain tool. I'm fine with it if Drago comes back as the villain, but if not, the villain should just be dragon hunters or rival dragon riders who use their dragons for conquering/raiding other settlements.

It can hit pretty much hit the same story beats as before but with better character dynamics.

Make Ruff and Tuff more instrumental to mischief and redirection in a way that helps the plot.

Give Fishlegs more credit for his discoveries and record-keeping about dragons.

Snotlout and Eret are together (or implied to be together if that's the best we can get). Snotlout is also no longer Hiccup's rival - he should be his second in command. They can disagree from time to time, but ultimately, his loyalty is not in question.

Fishlegs and Ruffnut have kids who cause chaos with Zephyr and Nuffink.

It would be cool to include a couple characters from other parts of the world with dragon mythology. I understand that Vikings are white but if we have goddamn flying dragons, there's no reason there can't be visitors from other cultures (who aren't villains).

Ending option 1: The movie can end with the dragons going away, but now they've been with the Berkians for over a decade and it just feels more impactful.

The "there were dragons when I was a boy" line can either be Hiccup talking to his grandson after an even longer time jump, or Nuffink talking to his own kids about Hiccup's adventures.

Ending 2: the Berkians go to The Hidden World with the dragons. Hiccup writes a memoir to leave behind. We hear him reading from it at the beginning and assume that means dragons are going to leave, but it's actually a diversion to make people think dragons are gone so no one tries to look for them.

Ending 3: We accept that HTYYD takes place in a different world so we don't have to explain why dragons don't live among us anymore. The movie ends with Hiccup vowing to make the archipelago safe for all dragons and Nuffink and Zephyr take up the mantle of discovering new dragons. The dragons stay and they all live happily ever after, the end :)

I'm tempted to actually write this as a fanfiction but I already got a lot of writing projects atm. We shall see.