The Amphi-Hydrus were one of several sentient species native to the planet Dac of the Outer Rim Territories' Calamari sector. They were small, physically weak amphibian beings with a squat body plan, green and brown skin, and orange eyes. They had four double-jointed limbs, with the hind limbs' toes being light-colored and blunt and the forelimbs featuring four sharp, black claws each. The Amphi-Hydrus were sensitive to the Force, being able to tap into its dark side.
At one point, the Amphi-Hydrus established telepathic control over several semi-sentient rancors that had been imported on Dac. Riding on their backs, the Amphi-Hydrus ushered in a brief period of chaos on their homeworld. When the Galactic Empire subjugated the planet around 19 BBY, however, the species retreated to the swamps of Dac, where they waited to gain power again.
The Amphi-Hydrus were created by Daren Horley through the "Design An Alien" competition run in the Star Wars Galaxy Magazine. The competition, launched in the magazine's third issue in April 1995, called for readers to create completely new alien species inspired by the original trilogy of Star Wars films. Harley was twenty-nine years of age when they submitted their entry on the Amphi-Hydrus, which was later published in the seventh issue in April 1996, under the "honorable mentions" section of the "16 and up" subdivision. Lucasfilm employee Leland Chee, who maintains the Holocron continuity database, later stated that published material from the "Design An Alien" competition was considered canon with respect to the Star Wars Legends continuity.