Entia the Shifter is the main antagonist of the book series, Unicorns of Balinor. He is said to be the most evil being in Balinor, and is called the Shifter because he can transform into anything, though only for a limited time. The evil Shadow Unicorns, led by Moloch, serve him, as do the snake woman, Lady Kylie, and the Shadow Rider. The Night of the Shifter's Moon (the new moon) is the time at which his magic is at its strongest, and no good magic will work.
When searching for Arianna, he is shown in the form of a sickly green eye, although his eyes are usually red. He also creates a shadow of his power to rule at the Royal Family's castle when he took it over. Forms Entia has taken include a large, muscular human (which is one of his preferences), a winged unicorn, dark smoke (which is quite a strain on him), a dragon, a wolf, a panther, and a batlike form.
The Shifter betrayed the Royal Family, kidnapped the king, queen, and princes, and stole the Royal Scepter. He also attacked Princess Arianna and her unicorn, Sunchaser, as they made their way across the Gap to the world beyond to escape him. His attack injured Arianna's legs and caused her to lose her memory, also causing Chase to lose his horn. The Shifter did not know how to cross the Gap, and searched for Arianna in the form of an eye.
Arianna eventually crossed back into the Gap and recovered Chase's horn, obtaining the final piece from the Royal Palace, which the Shifter had taken over. The Shifter killed one of his guards for not noticing them soon enough.
Ari's next task was to enter the Shifter's own castle, Castle Entia, in the Valley of Fear, and get the Royal Scepter back, as it was the key to awakening her memory and defeating the Shifter. Atalanta, the Dreamspeaker, and other Celestial Unicorns distracted him, getting Entia to chase after them in the form of a black dragon while Ari successfully retrieved the Royal Scepter. When she unwittingly crossed back through the Gap, the Shifter sent the Shadow Rider and Moloch (referred to in Book 4 as Moloth) to compete against her in the trial by fire, and the sea monster Sistern to try to kill her in the ordeal by moonlight, but Ari defeated both and overcame the trials.
Without the Royal Scepter, the Shifter was at a disadvantage. Desperate for power, he stole the powerful Indigo Star from Naytin the Dragon, although this was no easy task. He took away the power of the blue, indigo, and violet unicorns, including Atalanta, before Naytin woke up. Entia turned into a wolf and tricked the dragon into thinking that the humans of Balinor stole the Star. However he found himself unable to use its magic as long as Naytin was awake, for fear that the mighty dragon would kill him. Arianna once again entered his castle, this time disguised as a servant, and put the Shifter to sleep before stealing the Star back from him. Although he instantly woke up, Ari fought him off with the Star's power and returned it to Naytin.
The Shifter's last advantage was lost, and after the Royal Palace was taken back, the Shadow Rider revealed himself as Kraken, an ancient evil greater than Entia himself, blocking the power of his Watching Pool and threatening to kill him if he lost the upcoming battle. When Ari and her allies fought against the Shifter and his army, Ari unleashed the power of the Royal Scepter, and the Celestial Unicorns entered the battle. In a batlike form, the Shifter tried to attack Atalanta, but Numinor, the leader of the Celestia unicorns and mate to Atalanta, stabbed Entia in the heart with his horn. The other Celestial unicorns proceeded to spear him until he was no more. Castle Entia and the Valley of Fear were destroyed, and most of the Shifter's army, including Lady Kylie, were captured and imprisoned, although the Shadow Unicorns ran off.
Following Entia's demise in Book 7, Kraken becomes the antagonist in Book 8.
- The Shifter shares a few similarities to Sauron from Lord of the Rings.