A/N: Hello! All right then…this is the first time I've attempted a crossover so let's see how it goes. I hope you enjoy it!

Just a heads-up, this will have both movie and book characters. I've done my best to make sure everyone stays in character, but I do have to apologize: Wodensfang is going to be horribly out of character. I'm pretty much borrowing his name and attaching it to an original (sort of) character. Sorry, but it was the only way to make it work.

HTTYD belongs to Cressida Cowell and DreamWorks SKG.

The Little Mermaid belongs to Disney and is based on the fairy tale by Hans Christian Andersen.

Chapter One

Fathoms Below

The morning was quiet off the shores of Berk. A light fog had rolled in during the night, concealing the ocean in a layer of white mist. A flock of Terrible Terrors soared through the haze, calling and screeching to each other as they looked for a place to land. Down below, a Scauldron lifted its massive head from the sea, letting out a quiet snarl to warn the smaller dragons away from its territory. Knowing they were no match for the much bigger sea dragon, the Terrors flew away, a few of them squawking indignantly. The Scauldron snorted and then turned its head. It had sensed something else in the vicinity, something big…

That something was a Viking ship, which burst through the fog like some great beast leaping from its hiding place. The Scauldron ducked its head back into the water and swam away, suddenly wary. A ship could mean only one thing: humans.

And indeed, the boat was manned by a crew of about twenty Vikings, natives of the Isle of Berk, all laughing and singing cheerily as they threw their nets over the side, hoping for a good catch. Their rough voices carried over the misty surface of the sea, their song echoing in the stillness beyond:

"I'll tell you a tale of the bottomless blue

And it's hey to the starboard, heave ho

Look out, lad, a mermaid be waiting for you

In mysterious fathoms below"

There was much grunting and huffing as the Vikings pulled in their nets and started transferring the fish they'd caught into barrels positioned on the deck. It was a good catch: this would go a long way in stocking the storehouse on the island. Winter was on its way and they needed all the food they could possibly gather. The sea's generosity kept the mood on board light enough for the men to continue their song.

"Fathoms below, below

From whence wayward Westerlies blow

Where Stoick is king and his merpeople sing

In mysterious fathoms below"

As the men worked and sang happily, a young Viking girl of sixteen peered over the side, observing the foggy landscape. She was rather tall for her age, her blond hair tied in a simple braid that fell down her back, her blue eyes sharp and piercing. Her skirt was spiked and she carried her favorite axe in her right hand. She took a deep breath, ignoring the song still bursting forth from behind her ("Heave ho / Heave ho") and said to no one in particular, "Isn't this great? The salty sea air, the wind blowing in your face…" She sighed. "A perfect day to be at sea."

She heard a gagging noise from behind her and looked around. Snotlout Jorgenson was leaning over the opposite rail, currently losing his breakfast to the waves. "Oh yes…delightful," he muttered.

Astrid Hofferson rolled her eyes at her friend's sarcasm but didn't comment.

"A fine wind and a following sea," said a large man with a blond mustache and a hook for a left hand as he struggled to haul in another net. Astrid ran over to help him. "King Stoick must be in a friendly-type mood."

Astrid frowned at Gobber in confusion. "King Stoick?" she repeated blankly.

"Why, ruler of the merpeople, lass," the man replied with a chuckle. "Thought every good Viking knew about him."

From behind her, Snotlout snorted derisively. "Merpeople," he said, shaking his black hair out of his eyes. "What a load of dragon dung!"

Gobber the Belch glared at him and brandished a fish in his hand toward the boy. "Merpeople are real!" he insisted. "And Stoick rules over them! I'm telling you, lad, down there in the depths of the ocean they live—!"

He broke off as the ship lurched with a sudden wave. He staggered and the fish slipped from his grasp, hitting Snotlout in the face as it tumbled back into the sea. "Hey!" Snotlout yelped and Astrid put a hand up to cover her smirk.

The fish swam away the moment it returned to the water, not pausing lest it get caught in another net. The last strains of the Vikings' song were muffled and grew fainter as it descended into the endless blue:

"Heave ho

Heave ho

Heave ho

In mysterious fathoms below"

The fish made its way down toward the seafloor, weaving this way and that. It passed by a large rock formation and hid for a moment, waiting for a Scauldron to pass by before moving on. It had already escaped becoming a meal once that day. It didn't want to push its luck.

The next creature it encountered wasn't a dragon, but the fish still skirted away from it warily. From the waist up, it had the body of a human. From the waist down, the silvery tail and fins of a fish. A mermaid.

"Come on, we're late!" the mermaid called to her companions as she swam down into a crevice in the rock below. Two young mermen followed her, and the three friends emerged a moment later into the kingdom of Hyacinth, realm of King Stoick the Vast.

The merpeople swam as fast as they could toward the gigantic castle that dominated the scene before them: a magnificent structure made up of carved stone, glass, and coral. Behind the palace was a large courtyard, which was filled to capacity by a huge crowd. The sound of cheering and raucous yelling was deafening, but even that was drowned out by the screeches of the dragons being ridden in a giant loop around the village immediately surrounding the castle. In the center of the courtyard was an elevated platform, atop which sat the Sea King on a great golden throne. Stoick the Vast, King of Hyacinth, was a massive merman with an impressive red beard that reached down to his waist, where his skin melted seamlessly into the silver-green scales of his tail. He wore a golden crown atop his head and carried a large silver hammer in his right hand. Despite the weapon's obvious weight, Stoick carried it aloft seemingly with ease.

The king laughed cheerfully as a large dragon swooped over his head, sending his hair fluttering and swaying all over the place. The beast was carrying a rider atop its back: a small, wiry girl with long blond hair and a flashy blue tail. The girl was beaming toothily as she urged her mount toward the baskets that had been set up on the far edge of the courtyard. "Good girl, Fireworm!" she praised as the dragon unclenched its talons, releasing a bewildered octopus and dropping it into her bin.

"Another point for Camicazi!" Stoick roared over the cheers of the crowd. "That's my girl! She is currently tied with Fishlegs, leading with fifteen points! Dogsbreath and Speedifist lag behind with twelve points each, Wartihog has six points, Clueless has none, and Hiccup…" Stoick paused, frowning. The very first bucket, marked with a black ribbon, stood empty. He glanced around but there was no sign of his son or the boy's dragon anywhere. He sighed. "…is nowhere to be found," he concluded, and he added under his breath, "So what else is new?"

Camicazi leaned low on the back of her Monstrous Nightmare and called over to a stout boy riding a Gronckle, "Come on, Fishlegs! Gotta do better than that if you want to win this race!"

Fishlegs slapped his rust-colored tail in irritation at the princess' teasing and said to his dragon, "Come on, Meatlug. We still have a chance to win this."

The dragon grumbled worriedly to her rider but loyally went off in search for another octopus to add to their basket. At that moment, however, Stoick motioned for one of the guards to blow into a horn, the long note audible even over the racket in the courtyard. Fishlegs' heart gave a bound. He knew what that meant.

So did Camicazi. "The black octopus!" she gasped. "Come on, Fireworm! It's time to end this!" The Nightmare swam a little faster, her rider scanning the rocks below for a glimpse of the elusive cephalopod. The black octopus was worth ten points. She needed to find it and claim it in order to win this race…

There! The octopus was clinging to the underside of a rock shelf for dear life, apparently trying to hide from the dragons it knew were searching for it. But it had forgotten in its haste to hide that its tentacles, wrapped around the rock in a tight hold, were visible from above.

"You're mine!" Camicazi chuckled, but her smile faded almost at once. Fishlegs had seen the octopus as well and was already reaching out for it. Before Camicazi could do anything more than snarl in frustration, the stout merman had seized one of the tentacles and yanked the resigned octopus into his arms.

"Yes!" he cried. "Come on, Meatlug! Let's get back to the baskets, quick!"

The Gronckle turned around and started swimming as fast as her stubby legs would allow. But unfortunately for her and Fishlegs, she was probably the slowest dragon of all of them. Fireworm had no problem catching up, and Camicazi, with the skill of a master burglar, leaned over and plucked the creature from her opponent's grasp. "Gothca!" she crowed as Fireworm streaked away, leaving a bewildered and disgruntled Fishlegs in her wake.

Camicazi scored, and Stoick bellowed, "Camicazi wins the race!" A great cheer went up from the crowd, everyone looking up at the blond mermaid as she glided overhead, doing a victory loop and punching the water with her fist happily.

So no one saw Stoick as he looked away from his triumphant daughter, his eyes returning to the empty basket with the black ribbon. His smile faded and the hammer in his hand glowed an angry blue.

"Hiccup, where in the name of Thor are you?"

Hiccup Horrendous Haddock the Third peered excitedly at the ghostly wreck that lay before him. He wondered what had caused the ship to sink. A storm perhaps? Or maybe it had been involved in a fight with another boat? It was impossible to tell from looking at it: the wooden hull was rotted and cracked in several places, and the central mast was missing entirely. Still, it looked as though it might hold some interesting secrets, secrets that Hiccup wanted to discover.

He glanced over his shoulder, brushing his auburn hair out of his eyes with an automatic swipe of his hand. His bright emerald eyes landed on the black dragon drifting a few yards back. "Come on, Toothless," he called. "Let's get a little closer."

The Night Fury warbled and swam a little closer. Though a sky dragon, he (and indeed all dragons) could breathe underwater thanks to a set of gills situated behind his ears, but his swimming wasn't as graceful, fast, or agile as his flying. His wings were designed for air, not water. However, he joined his merman friend fairly quickly and crooned questioningly, looking in obvious doubt at the wreck.

"Of course I'm sure," Hiccup replied. "Let's take a look!"

With a flick of his green fins, he propelled himself toward the sunken mass, grinning excitedly. Toothless followed, his luminous green eyes alert and watchful for danger. He could smell another dragon not too far away and wanted to make sure no harm came to his friend. Hiccup either didn't notice or disregarded the Night Fury's unease, slipping over the edge of the vessel and scanning the deck for any treasures he could take.

His eyes fell immediately on what looked to him like some kind of shell. Or half of one anyway. It had a flat bottom and rounded sides and was open at the top. It was, in fact, a bowl, but Hiccup had never seen one before and had no clue of its purpose. "Whoa," he breathed, bending down to pick it up and studying it intently, a toothy grin spreading across his face. "Wow, look at this bud! Have you ever seen anything so wonderful in your entire life?!"

Toothless eyed the bowl quizzically and grumbled, clearly not impressed. "You're no fun," Hiccup remarked.

Toothless warbled, and even though Hiccup couldn't understand the dragon language, he got the general gist of the question and shrugged. "I don't know what it is, bud. But I bet Wodesfang will." And with that he shoved it into a bag he had slung over his shoulder, another item he'd discovered on his secret expeditions. It had the emblem of a black dragon on it, which reminded him of Toothless, and it was one of his most prized treasures.

Toothless sniffed the water and growled softly. That other dragon was getting close. Hiccup didn't hear him, his focus now on an item that looked a lot like the bowl, only it was adorned with a metal band around the rim and had two horns sticking out the sides. "Hmm," he mused as he picked up the Viking helmet. "I wonder what this one is…"

Toothless roared, and Hiccup finally looked over at him, alert. He knew that was a sound his dragon made only when there was a threat nearby. "What is it, Toothless?" he asked, looking worriedly about.

Toothless didn't have to answer. Hiccup suddenly knew exactly why the Night Fury was so on edge. There was another dragon swimming their way, a Thunderdrum. Its beady eyes were narrowed in hunger and its mouth was open, preparing to emit its powerful sonic roar.

Despite the fact that merpeople had made peace with the dragons that lived in both air and water, Hiccup felt his heart miss a beat. This was clearly a wild dragon, and wild dragons were, as the title suggested, unpredictable and dangerous. And right now, it clearly saw the young merman's fish tail as quite a tempting meal. Hiccup, knowing better than to try taming or training it while he was viewed as the main course, hurried over to where Toothless floated, growling up in warning at the newcomer. The great blue dragon didn't even slow in its approach. It roared, the sound echoing and reverberating in the otherwise silent waters. Hiccup brought his hands up to cover his ears as Toothless shot forward. Were they in the air, he'd have been able to fire a plasma blast that would surely have sent the other dragon fleeing in terror. But in the water, a dragon was unable to use any firepower.

That didn't stop him from using his teeth, however. Toothless latched his jaws on one of the Thunderdrum's feet, and the blue dragon immediately cut off its roar to shriek in pain. It lashed out with its long, ropy tail and struck Toothless in the face. The Night Fury let go with an aggravated growl and retaliated by tackling the bigger dragon, sending it down to the deck of the Viking ship below.

"Toothless!" Hiccup cried, his voice lost to the crash of splintering wood and the angry roars of the two fighting dragons. He swam forward, peering anxiously over the side of the ship to see the Thunderdrum flat on its stomach with Toothless crouching over him, pinning him to the seafloor, teeth bared. The Night Fury roared loudly, and the defeated dragon squirmed, lowering its head submissively, apparently waiting to be torn apart by the victor's claws and teeth.

Toothless snorted, satisfied that the Thunderdrum wouldn't pose a threat anymore, and backed off. The other dragon swam away at once, as if afraid the Night Fury would change his mind and attack again. Toothless watched it depart and then turned back to Hiccup, his green eyes narrowed, silently scolding his friend.

"Thanks, bud," Hiccup said, swimming forward and scratching the dragon under the chin, something he knew Toothless loved. "I didn't even see him coming."

Toothless snorted again, and Hiccup added, "Yes, I know, I was reckless and should have been more attentive." He sighed. "But you know how I am."

The dragon rolled his eyes but seemed to be content to let it go. His pupils dilated and he crooned fondly, nudging his friend. Hiccup chuckled. "All right, bud. Let's go on up and see what Wodensfang has to say about what we've got this time." And with that, boy and dragon began swimming up toward the surface.

Wodensfang was a little dragon, a Terrible Terror to be precise, who had the unique distinction of being the only dragon to have mastered the Norse language, which both merpeople and the humans on the nearby island of Berk used. He was snoozing on the little outcropping of rock he had claimed as his nest, happily dreaming about the large meal of fish he hoped to find that evening, when he heard someone call his name. He woke with a snort, smoke trailing up from his nostrils, and looked around. His big yellow eyes brightened at once. "Hey, merman off the port bow!" he crowed, rising to his feet and scurrying to the edge of the rock, where Hiccup and Toothless had emerged. He tripped once over his own feet and went tumbling, making Hiccup chuckle and Toothless, who had minimal patience for the tiny dragon, snort in irritation. The clumsy Terror regained his footing almost at once. "Hiccup, how ya doing, kid?"

"I'm fine, Wodensfang," Hiccup replied, lifting the bag off his shoulder and depositing it on the rock. "Look what we found!"

"Human stuff, huh?" Wodensfang inquired, sniffing the bag curiously. "Well let me see…" He stuck his snout into the bag and pulled out the bowl with his mouth, his toothless gums clamped on the rim. Releasing it and looking down at it, he said, "Wow…this is special…this is very, very unusual…"

Hiccup barely suppressed an eye-roll. Wodensfang was notorious for talking to himself and totally forgetting that there were others around him. "What?" he asked, unable to contain his excitement. "What is it?"

Wodensfang, apparently remembering the merman's presence, looked up and announced, "It's…a dinglehopper!" He took the bowl's rim in his mouth again and flipped it up into the air so that it landed on his head like a hat. "Humans use these things as a way to protect their heads from the sun!" he explained. "You see, human heads are delicate, and the sun is hot enough to make it turn bright red, which makes them very unhappy…it looks bad, you understand? So they use these dinglehoppers to cover their noggins and keep them the right color."

"Wow," Hiccup sighed, totally in awe as Wodensfang flipped the bowl off his head and nudged it back over to the merman, who picked it up and studied it fondly. "A dinglehopper!" He put it back in his bag and pulled out the helmet. "What about this one?"

"Ah!" Wodensfang bent his head down and sniffed the item excitedly. "I love these little babies! This…" He puffed himself up importantly. "…is a banded, bulbous…snarfblat!"

"Ooh," Hiccup breathed, impressed, as Wodensfang did as he had with the bowl and flipped the helmet onto his head.

The dragon explained, "The snarfblat dates back to prehysterical times, when humans used to sit around and stare at each other all day." To demonstrate, he pushed his face up close to Hiccup's so that the merman was staring right into the Terror's bright, luminous eyes. He blinked, feeling slightly dizzy. A dragon's stare could be hypnotizing. "Got very boring," Wodensfang added. He drew back, and Hiccup shook his head slightly to clear it. The dragon didn't seem to notice the merman's discomfort. "So they invented this snarfblat to pass the time. It's a noisemaker, see?" He whipped his tail against the helmet, making it clang and vibrate on his head. "W-w-h-h-oooo-ooooaaa," he said tremulously, his head swaying dizzily. Hiccup clapped a hand over his mouth to stop himself from laughing.

"Yep," Wodensfang continued after shaking his head vigorously. "Humans use these things whenever they get bored. They are particularly popular at big social events like parties or gatherings…"

"Parties?" Hiccup repeated, his face suddenly going blank. "Gatherings?" Then he groaned and smacked his forehead with his palm. "The race! Oh my gods, my dad's gonna kill me! I forgot the race was today!"

Wodensfang didn't seem to notice Hiccup's sudden realization. "Maybe you could make a little planter out of it or something," he mused, looking down at the helmet he had tossed on the rock at his feet.

Hiccup snatched the helmet up and stuffed it into his bag. "I'm sorry, I've gotta go!" he said hurriedly, turning and swimming a short distance away from the rock. He paused and called back over his shoulder, "Thanks, Wodensfang!" before diving into the sea, Toothless following close behind.

"Anytime, pal," the Terror called to the empty ocean, waving one wing absentmindedly. "Anytime."

Once beneath the waves, Hiccup climbed atop Toothless' back, leaning down and saying in the dragon's ear, "Let's go home, bud. Maybe Dad won't be too mad this time…"

Toothless warbled and took off, swimming as fast as his feet and tail would allow. Hiccup held on to the dragon's shoulder blades, praying to every god he knew of that he could slip back into the kingdom without attracting unwanted attention.

He didn't know he was being watched.

Outside the borders of Stoick's kingdom, in a desolate wasteland, two creatures sat in the ribcage of a massive dragon skeleton. One had the upper body of a pale, thin woman with long white hair and horrible yellow eyes. Her teeth were half-rotten and crooked and her fingernails were long and sharp. She wore a spiral shell necklace that rested against her rather flat chest. From the waist down, her body morphed into that of an octopus, eight purple-black tentacles twisting and writhing along the seafloor. The other creature had the head and torso of a painfully thin young man with lank black hair and sharp, wary eyes. He was so skinny that his ribs showed plainly through his faintly-yellow skin. His lower half was the body of a green eel. Both of these creatures were staring down at a massive stone cauldron that sat in the middle of their home. An image shimmered above the mouth of the pot: a young merman, bag slung over one shoulder, riding atop the back of a black dragon, streaking off in the direction of Hyacinth.

The woman, Excellinor the Sea Witch, smiled coldly at the image. "Yes," she hissed, "hurry home, dear prince. We wouldn't want to miss the celebration of your little sister's win, now would we?" Her smile vanished and she laughed once derisively. "Celebration indeed! Bah! In my day, we had fantastical feasts when I lived in the palace…"

She sighed and looked across the cauldron at her son, Alvin the Treacherous. "And now look at me," she moaned. "Wasted away to practically nothing…banished and exiled and practically starving, while he and his flimsy fish-folk celebrate." She scowled and looked again at the image of Hiccup and Toothless. The prince and his dragon were now on the outer borders of the kingdom. The Sea Witch hummed thoughtfully. "Well, we'll give them something to celebrate soon enough, won't we Alvin?"

The young man across from her smiled darkly.

"Yes," Excellinor said, her smile returning. "We'll have to keep an extra close watch on this handsome little boy of his. He may be the key to Stoick's undoing…" She chuckled darkly and returned her attention to the image above the cauldron.

Yes…she could be patient. Their time would soon come…