MagiStream

I noticed there was not a legend for the Hippocampus, so I thought I would take a swing at it.
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How the Hippocampus Came to Be

Long, long ago, when the trees of the Silvia forest were young, and the Arkene was not covered in ice, there was a boy called Jareth, and he had the most beautiful horse called Elsu.
Elsu had a coat like white marble. His mane and tail were long and gleamed in the sun like white waves. But, above all, he was the fastest of all horses, able to outrun even the mighty dragons, and his endurance was uncanny, allowing him to gallop for many hours on end.
Jareth and Elsu loved one another very much. Jareth never put a bridle or saddle on Elsu, and Elsu was always willing to carry the boy wherever he pleased, as both of them were very adventurous.

One day, Jareth asked his father to allow him to go to the mountains. He longed to have a dragon, and he had heard that they kept their eggs in high places.
“Don’t be absurd!” his father said “However would you climb those mighty mountains?”
“Elsu will take me, father. He is the most surefooted of any horse.” Jareth insisted.
“I forbid it,” his father replied “It is much too dangerous. Dragons are dragons, and men are men. Let it stay as such. Besides, Elsu is a horse which many men desire. Be content with him and do not desire something greater.”
But Jareth would not be content. For many days he fumed silently until he was no longer able to control himself. “I will have a dragon to call my own, even if it is the last thing I do!” he told Elsu “My father does not think me capable of such bravery and strength. I will prove him wrong!”
That night, he mounted Elsu and asked the horse to take him to the mountains. Elsu hesitated and argued with Jareth, but, unwilling to displease his friend, he finally consented. He galloped through the night until they reached the mountains, then he carried Jareth up to the peaks and the two of them wandered the mountains for many days until, at last, they found a dragon’s nest.

Jareth took great care in planning how he would steal an egg, but he underestimated the vigilance of a mother dragon. He carefully made his way up to the very edges of the nest, undetected, but as he reached out to take an egg for himself, the dragon spotted him.
In her rage, she grasped him into her talons, meaning to tear him to pieces.
Elsu came to his rider’s aid and called out fearlessly to the dragon. “Oh mighty dragon! Please do not harm my rider!”
“He violated my nest!” the dragon snarled “He will pay for his crime!”
Elsu shook his mane and reared, pawing the air. “Then I would challenge you to a competition, oh dragon!”
The dragon was intrigued. “A competition? What does a puny horse have that can compete against me?” she demanded.
Elsu scraped his hooves across the earth. “I am the speediest of all creatures, even of those that fly in the sky. If you can beat me in a race of speed and endurance, then you may punish the boy. If I win, then you shall give him to me, unharmed.”
The dragon, thinking this an easy win, accepted his challenge.
“We shall race down the mountain, through Silvia Forest, and the first to reach the ocean shall be the winner.” Elsu said.

The dragon left her mate to guard the nest and, holding Jareth safely in her claws, she gave the mark, beginning the race. At first, she lazily glided in the sky, thinking that the horse, a land animal, was no match for her, but as Elsu kept pace with her she began to worry. She beat her wings harder, and still Elsu kept stride with her. She rose higher in the sky, catching the wind currents, but Elsu pushed his nose forward and pumped his legs faster than ever. The dragon began to beat her wings rapidly, determined not to be shown up by a mortal creature. However, Elsu, out of the love for his rider, gripped the ground harder and forced his muscles to move faster than they ever had before.
For a day and a half the two raced, neck and neck, down the mountainside and across Silvia forest with incredible speed.

As they neared the ocean, the dragon began to panic. She could not live with the shame knowing that she had been beaten by a mere horse. She dropped low in the sky and began to try and disrupt Elsu’s stride. She struck at him with her talons, ripping out his long, beautiful mane, but Elsu’s pounding hooves never missed a beat.
Again, the dragon tried to mar his stride and sought to seriously wound him. As her talons neared his glistening white back, Jareth cried out to Elsu, directing him to veer away. Elsu heard his master’s cry and swerved, barely missing the deadly swipe of the dragon’s claws.
Finally, with the ocean very near, the dragon became desperate. She rose into the sky and let out a long stream of flames, directly into Eslu’s path.
Elsu jumped over the flames, burning his long, beautiful tail, but he did not stop. He hit the ground running, forcing his legs to move faster than ever.
The dragon beat her wings harder than before on the final stretch of the race, but Elsu stayed with her, his hooves pounding the ground with such fury that it caused the earth to rip under him. The two of them reached the shore at the same time, and together, hoof and claw, they touched the waters of the ocean simultaneously.

The dragon was furious, but she looked at Elsu with new respect, impressed by his strength. “You have surprised me, small one. Your endurance and courage are great, as is your loyalty. For that, I shall give you a second chance to save your rider.” she smiled deviously “You run very fast, but tell me horse: how well can you swim?” with that, she jumped into the sky and flew far over the ocean. When she was far enough out that she was certain Jareth could not swim back to shore on his own, she released him, letting him fall into the water and to his certain death.

Elsu screamed and pounded the beach angrily, and he watched as the dragon flew away, back toward the mountains. He rushed out into the water and began to swim with all his might, but his swift legs were no match for the waters.
“Oh, my rider is lost! My rider is lost forever!” Elsu began to weep and wail as he continued to swim.
Suddenly, the ocean waters rose up before him, forming into the shape of the sea god. “Why do you weep, child of earth and wind?” the god asked “Why are you in my domain, the sea?”
Elsu cried out in great despair. “Oh great ruler of the sea! My rider, whom I love dearly, has been taken from me by a dragon and dropped into your waters. I have raced the dragon from the mountains, across the forest, through her flames, and to the seashore, but she would not give me back my rider. Now he is dying and there is nothing I can do to save him.”
“Oh?” the sea god asked “The goddess of the wind and father earth has seen your impressive display of speed and courage, and they have told me of it. I will give you the gift to traverse my domain with the same speed and endurance that you displayed before. I will give you what you need to save your rider. However,” he paused and leaned in close to Elsu “If you accept my gift, you will not be allowed to return with your rider and gallop on the land as before.”
For Elsu, the god’s warning had no meaning to him. “I care not what happens to me! Just help me save my rider from death!”

The god fell back into the ocean, and Elsu was left alone. He kicked against the waves with unwavering determination, finding that he was becoming faster and stronger with each stride. Soon, he felt that he and the waters had become one. Faster and faster he went until his sharp ears heard Jareth’s cry and his far seeing eyes spotted the boy, barely afloat, sinking beneath the swelling waves. Elsu reared in the water and plunged under it, swimming faster than he knew he ever could. He found Jareth and swam under the boy, lifting him up out of the water, then he began to swim for shore.

When his feet touched land, Elsu instantly felt the difference. It became difficult to move. His back legs did not work as they once did. His muscles struggled to pull him away from the waters until, finally, he could make it no further and he collapsed onto the beach with Jareth.
“Elsu! Oh my poor, dear Elsu!” Jareth cried when he had breath again to speak “What has happened to you? What have you done to save my life?”
Instead of powerful back legs and a charred tail of hair, Elsu now had a long, bright fish tail. His coat of white marble was slick and soft, and his damaged mane had grown back and was filled with seaweed.
Elsu now understood what the sea god had meant when he told him that he would never be able to return with Jareth.
Having saved his friend, and unable to bear long goodbyes, Elsu gave Jareth a tearful hug and plunged back into the water’s embrace. Jareth sat on the beach and wept for many long hours, wishing he could undo all that had happened.

Over the months, Jareth returned to the beach often in search of Elsu, but he never saw his friend again. Knowing that his foolish actions had caused Elsu to make such a sacrifice, Jareth sought to make his friend’s life in the ocean as happy as possible. He gathered together a herd of the very finest horses that could be found, horses with the shiniest coats, the swiftest legs, and the most endurance and intelligence. He brought them to the ocean, to exactly the place where he had last seen Elsu, and then he called out to the god of the sea. “I must repay the debt that I owe my dear friend, Elsu, who once was a horse but now swims in the waters. I have brought these horses for him, so that he might never be lonely. Please, I ask that you let these join him, so that he might be happy.” he led the horses out into the ocean until the water had risen to his chest, then he waited. After a short time, the horses each began to jump and squeal in excitement until they all jerked away from him. They charged out into deeper waters, their appearances gradually changing. Suddenly, they jumped into the air, flipping long, bright fish tails behind them, showing Jareth that his prayer had been answered.
They splashed back into the water and their figures rose and fell as they swam further and further out to sea. As Elsu watched, through his tears, he thought he saw a brilliant white Hippocampus join them with a joyful whinny. Then they all swam away, out of sight, never to be seen again.
Thus, was the great Hippocampus species born.

Excellent! The only edits I can suggest would be to change 'wept sadly' - seems kind of unnecessary - and right at the beginning 'ridiculous' is misspelled. But apart from those few things, I think it is a lovely tale, the kind I could imagine young children being told

Once again, thank you so much for the helpful suggestions! I have changed them now.
I was happy it turned out so well, since I was very sleep deprived when I wrote it. It's amazing what inspiration sleep deprivation can provide. Haha...