Indigo or "Indi" as he is better known as, is a shap-shifting power crystal who stayed in the form of a purple and blue unicorn stallion to bond with Emily and become her paladin. Indigo was inspired by Shadowsong in Princess Gwenevere and the Jewel Riders, where there was also a character named Indigo.
Emily first met Indigo when he shape-shifted into a purple sea dragon pup when she attended the Wave Fest in Aquatania (in Heart of Avalon). She, Prince Marlin and Indigo were then blown off to an island called Port Tuga (on the Giant's Footpath) where Indi became a purple ferret, pretending to be Ozzie. Emily noticed something strange, but was just happy Ozzie was there with her. Until, "Ozzie" ate everything in her backpack, then ate the jewel right off her bracelet. Indi kept shape-shifting with her and Marlin as they went to a thief auction, and scared off the bulwoggles as they boarded the boat. On an island, supposedly at the Gates of Avalon, she found Indi in his true form, an ugly-looking, gray blob, dragging its tail behind it. Thankfully, Emily still saw the beauty in Indi, who promised to always be by Emily's side spiritually.