Waterhorse Dragons received their name due to their horse-like physique and endearing behavior. They are capable of surviving out of water, and when on land their skin secretes a gelatinous goo to retain moisture. However, their large paddle feet are better suited for swimming, and waterhorse dragons tend to move very awkwardly when on land. Waterhorses are very friendly dragons and enjoy playing with humans.

Dragons are highly-intelligent reptilian creatures that—from a human perspective, at least—appear to live forever. Many different varieties of dragon exist, each with their own unique qualities, habitats, and behavior. Adolescence in dragons is usually marked by the growth of a hatchling’s wings, although not all breeds of dragons grow wings and some breeds have other traits that indicate the beginning of maturation. In Galsreim, dragons and humans coexist peacefully.

When he was out for a swim one day, the sight of Placidnon's egg caught the attention of Platino. The egg was beautiful and Platino was very eager to hatch it. The hatchling came out strange, almost mutant for a dragon, but nonetheless became a great swimming partner for Platino. Placidnon enjoys swimming in coral reefs, chasing fish and collecting things for Platino. He is very protective of a coral reef near Platino's home and becomes quite agressive with anybody who invades it.

Placidnon's name is denunciated from the word "Placid".