Flight (Rewritten) has HTTYD2 and RTTE canon, but nothing from HTTYD3.
The three pieces of film I keep most solidly canon within my accepted 'canon' are the original HTTYD, Gift of the Night Fury and Legend of the Boneknapper Dragon. I've only accepted bits and pieces of HTTYD2 and any of the TV shows as my 'canon'.
HTTYD (c) DreamWorks.
The cold morning air stabbed at Hiccup's face, throwing his shaggy brown hair around his head crazily, his mask having been forgotten at Berk.
Toothless's wings beat against the wind strongly, the subtle shifts and twists of his wings flowing through Hiccup's legs, earning a sense of nearness he had not been able to fully appreciate since he had become chief. Toothless seemed to be enjoying the flight almost as much, if not more, then Hiccup, his large pink tongue lapping out in contentment throughout most the flight.
"This feels great doesn't it bud?" Hiccup yelled over the wind to the black dragon, who warbled raucously in response. "Yeah that's what I thought!"
Hiccup brushed his hand against Toothless' head, shaking the ear plates slightly as a familiar squawky dragon call bubbled from behind him. Hiccup turned backwards, a joyful smile crossing his face at the sight of Astrid, her woolly hood pulled over her head, and her cyan colored Nadder, Stormfly, quickly catching up to where he and Toothless were.
"Good day, Astrid," Hiccup said, giving her a crooked smile that she returned back to him.
"Good day to you, Hiccup. I saw you leaving Berk and I had to follow you," Astrid replied as she brushed a lock of blonde hair out of her eyes unconsciously.
Hiccup smiled loosely, turning Toothless slightly towards Stormfly. "Yeah, Dragner was being really annoying and I had to get out of there before I went insane."
Astrid rolled her eyes at Hiccup's response, her blue eyes smoldering with anger. "I still can't believe you let Dragner be your second-in-command Hiccup, even if he was Gobber's apprentice," the blonde Viking mumbled as Stormfly thrust her wings downwards powerfully, lifting her body slightly. "You could have even appointed Eret."
Hiccup frowned narrowly, the corner of his eye catching on a small sea stack below them "Why don't we land? Stormfly looks tired and I could use a bit of a stretching. Then we could talk."
"Fine."
Stormfly squawked happily as Astrid urged her forward with a sharp nudge from her legs, down to the sea stack. Hiccup followed close behind, Toothless grumbled in protest as they landed on the sea stack. Securing Toothless's tail, Hiccup clambered off his dragon and walked up to Astrid who had nimbly leapt off Stormfly and was leaning against her wing.
Hiccup brushed his fingers along Astrid's face, pushing a long strand of hair out of her face. "You know he was most qualified to be second-in-command, after you of course. Mother could never run Berk and Ruffnut and Tuffnut are too scatterbrained to run anything without destroying it. Dragner was my best option. He's a good guy."
Astrid shook her head, moving away from Hiccup, who followed behind her slightly, "I don't know Hiccup. Dragner... I don't trust him at all. He seems too angry and bitter to be able to lead to me and he doesn't even have a dragon. Even Spitelout had a dragon, but Dragner does not?"
"Well he told me that he hadn't figured out the breed for himself, Astrid. He will get a dragon, and I trust him," Hiccup urged, grasping at his wife's arms gently. "Trust me, Astrid. Trust me like you always have."
Astrid groaned, her blue eyes turned downwards, her mind seeming lost in thought until she grumbled, "Okay. Just this once, Hiccup. And only for you."
"Good!" Hiccup smiled in Astrid's direction, lowering his hands to his side as Toothless walked up to him, rubbing his broad snout against his hand. He glanced up at the sky, just noticing how much the temperature had fallen and the sky had darkened since they had landed. Hiccup could feel the coming cold seep into his bones, a telling reminder of the ever present threat of snow in the Archipelago. Small puffs of white came from Hiccup's mouth as Toothless curled a large wing around his body, the welcome warmth from his dragon refreshing from the cold.
"We should head back, Hiccup. I need to get Eris and Stoick back from Ruffnut and it's getting cold out, Stormfly is freezing."
"Yeah... Let's head back," Hiccup said as he and Astrid climbed onto their respective dragons, Stormfly and Astrid taking off first.
Toothless groaned in protest as Hiccup hooked his leg into the final adjustment lever and clicked his tail back into place, the black dragon shooting off the sea stack after the Nadder.
Hiccup and Toothless caught up to Astrid and Stormfly, Toothless cooing jubilantly as he sped up, leaving the Nadder behind. Hiccup laughed softly, looking back in time to see Stormfly rocket past him, Astrid leaned over her dragon's neck, a determined scowl on her face.
"Oh, it is on Astrid!" Hiccup called after her, adjusting Toothless's tail fin for a speed boost. Toothless shot forwards, zipping past Stormfly with an expert barrel roll. Astrid's roar of shock and indignant anger bolted after Hiccup and the unmistakable sound of Stormfly shooting after him soon accompanied Astrid's anger filled growl.
Toothless and Stormfly chased each other, Astrid yelling threats to Hiccup about him daring to beat her and how she "would get him back for it", until a quiet silence broke between the two Vikings. Hiccup and Toothless slowed, letting Stormfly catch up to them as they headed back to Berk, the cold wind biting through Hiccup's leather riding suit, chilling him to the bone.
"It might snow tonight, judging by this wind," Astrid commented, looking towards Hiccup, who nodded curtly in response.
"When we get back I will get Eris and Stoick from Ruffnut and would you get the villagers to move their dragons into their stables and close all storm doors?"
"Of course."
"Thanks Ast-" Hiccup's voice was cut off when Toothless's head shot up suddenly, ear plates standing straight upwards. "What is it bud?" Worry wormed through Hiccup as the Night Fury glanced sideways, his mouth curled into a snarl, ear plates quivering. The air temperature seemed to drop even more as an eerie feeling of fear crept through Hiccup's skin as Toothless's entire back bristled, and Stormfly's tail spines snapped up, the Nadder's jaws bared into a snarl.
A sudden roar ripped through the air, causing goosebumps to run down Hiccup's body just as something huge shot from the clouds, its entire body coated with flames.
"Nightmare!" Astrid cried just as Stormfly folded her wings to her body and shot downwards, the tip of Nadder's tail just barely missing the snap of the huge, black talons of the Nightmare. Toothless roared in response, diving after Astrid and Stormfly swiftly, his wings folded flat against his body as the unmistakable beat of the Nightmare's wings followed behind him. Hiccup glanced backwards in time to see the Nightmare catching up to him, its yellow eyes filled with hatred as flames stoked within its jaws. Toothless swerved as the Nightmare snapped its talons towards him, its talons just brushing against Toothless' tailfin, though it was enough to jar Toothless' body. Toothless snapped his tail from the Nightmare's talons then wheeled on the Nightmare, a roar escaping from the black dragon as the Nightmare's jaws snapped near him once more.
Toothless let out another roar and, with his ear plates flattened to his skull, opened his jaw, flames building within him, readying a plasma blast. Toothless was about to loose his blast when Hiccup's eyes caught on- a stirrup? The Nightmare has a rider?
Hiccup jerked back on Toothless, interrupting his dragon's shot enough that it just barely grazed the Nightmare's horns. The Nightmare snarled and then lowered its head closer to Hiccup, giving him the chance to see the armored rider astride the Nightmare. A thick red coat made of dragon scales was draped over the rider's armored shoulders - armor that was made of red dragon hide and scale and made to resemble the Nightmare the rider was astride. The rider looked down at him, their expression hidden by the helmet they wore but, as Toothless let out another warning snarl to the Nightmare, Hiccup suddenly recognized the eyes that glared back at him and the black horns that twisted from the Nightmare's skull.
It was the dragon he had been tasked to kill fifteen years ago in the Kill Pen, the Nightmare who he had given to a man he had once considered a friend, an ally, and a man who he had not seen since his exile ten years before.
"Hookfang? Snotlout?!"
Updated once again for grammar and other issues.