Origin

When people first took to the seas the Waterhorse did not exist. No one is sure if this story is accurate, but it is what all young Waterhorse learn about their creation. A male dwarf decided one day to sail the seas. He was warned that being unable to swim and being so dense, that he would drown during the first storm. Well, this was mostly said in jest, but a female dwarf heard this and knew the risk. She loved this would be sailor and made up her mind to follow him, join his ship and make sure he remained safe. Sailors were still superstitious, and when they figured out this second dwarf was a woman, they blamed her for all their misfortune, and they deemed her life was forfeit. When the male dwarf argued to defend her, he was punished as well. Together they were thrown overboard. They clung to each other as they tried to stay afloat. This entire encounter had been witnessed by a curious archfey, who decided that day to be kind. As they used all their strength, and dropped below the surface of the water, they did not die. Suddenly they were not dwarves. They looked like the sea monsters they feared encountering on the ship. And they heard a voice in their head telling them to enjoy the depths, but not to forget the land that they once called home. Together they explored the depths of the sea, learned their limits. The possibilities seemed endless, but they became homesick for the green grass of their home. So they remembered the voice and went to land. They found a beach, and as the tide receded, they found themselves naked and bipedal. They looked just like they had before being thrown off the ship, only they'd lost their hair and their flesh looked blue. And they laughed, knowing they could have whatever world they wanted.

Appearance

On land: They are bipedal humanoids that are about the same size and shape of a dwarf. They weigh a little bit more on average, but that is mostly because their skin is made of tough denticles that gives them a level of natural armor. Those denticles also tint their skin blue, but the hue will vary a little depending on where in the water they spend the most time.

In water: They transform into a plesiosaur in the water. A large sized aquatic mammal, with four fins, a relatively short tail, and an exceptionally long neck. They defend themselves with their massive body and a jaw full of sharp teeth. Their skin varies in color depending on where they live, with it being lighter and brighter the closer they are to the surface.

Mannerisms

On land: They are deeply curious. Many Waterhorse have not seen many things that are considered commonplace for even a child. You might find them staring at a tree for hours, but they are also highly intelligent so those hours might result in them discovering a new medicinal property of the bark. This often makes them relentlessly optimistic and willing to try anything at least once. Since most Waterhorse are younger when they spend large amounts of time on land, they are also less weary with humanity. They don't mind talking to gnomes about tinkering or  druids about flowers. If you find it fascinating, they will also be interested in learning more, even if it is only to satiate their curiosity about why you like it. Their friendly and trusting nature can lead them to being taken advantage of or conned.

In water: They are much less curious in water than they are on land. It is all so familiar that rarely do they encounter something to pique that curiosity. The closest thing they have are occasional shipwrecks, so during storms, many will trail ships to make sure any hapless sailors don't drown. They doubt that a kind fey creature will transform the sailors, so they do what they can to keep people safe. Though generally gentle and kind, they are not pushovers. Many of the elder Waterhorse are valiant protectors of the deep, and often serve as true allies of the Triton. And they will protect themselves, their homes, and their allies with everything they have.

Habitat

On land: they are often nomadic, enjoying sleeping under the stars and the sounds of chirping insects. Accustomed to the wide open oceans, being inside for too long is uncomfortable, and the sprawling cities are not much better.  An open field or dense dark forest is ideal, though small quaint towns can be nice too. When they go to land they don't generally live among their own kind, preferring instead to learn from other kinds of intelligent life.

In water: Most prefer to live near land when they can, so they will settle right near drop offs. The spot just beyond reefs that take sudden dives into the depths to give them plenty of space, but keeps them near enough to land to visit it whenever they would like to. However some prefer to live within the reefs proper or even in far deeper waters away from land and people. They live in small clans, and seek out other clans for the sake of breeding. These clans determine where they will settle and what type of protection is more favorable. If they encounter a larger, more territorial predator, they will seek out a new home, but anything smaller than them can usually by scared away or fought off.

Adventure?

The Waterhorse are often overwhelmed by the intense curiosity to see parts of land beyond what is visible from the sea. They have heard from their returning fellows about weird and wonderful sights.  Far flung lakes that are utterly surrounded by land, deserts that have no water for miles, forests with trees so dense that the stars aren't visible from the ground. All of these inspire the young to travel forth. The friendships formed from the first time traveling often inspires others to return to land. It is often lonely on later trips because they age so slowly in the water that many of their friends are now aged, ill, or dead. But as generally friendly creatures, they make new friends easily and take death better than many.