"The Mystic Isles: The Mare of the Mist" is the eighty-ninth episode of the Disney Junior animated series Sofia the First. It premiered on August 4, 2017 and is the eighth episode in the fourth season.
Sofia is flying through the sky on Minimus when Skye suddenly arrives with a crash. Chrysta also flies in and tells her it is time for the next phase of her Protector Training: Getting her WhichWay Bow. The WhichWay Bow is a Protector tool that shoots a magical arrow that tells the shooter which way to go somewhere. Sofia needs to get the bowstring for hers from the Mare of the Mist on the Isle of Unicorns. Since she cannot fly unassisted, Sofia needs a Protector Steed and Skye has volunteered. Jealous of the affection Sofia has shown Skye, Minimus also volunteers to be Sofia's Protector Steed. Hearing this, Chrysta asks Sofia to choose between "the unicorn and the flying donkey." Due to past experience, Sofia does not want to choose between an old friend and a new friend so Chrysta tells the two horses that whoever does the better job during Sofia's mission gets to be Sofia's Protector Steed. They take off and, on the way, Minimus and Skye have a spat for Sofia's affections.
They arrive at the part of the Isle of Unicorns known as the Veil of the Mist. Chrysta tells her she has to get one of the Mare of the Mist's hairs for her bowstring by sundown and because she is skittish it will be difficult. Sofia rides off on Skye with Minimus following. They find her but Minimus and Skye have another fight that scares the Mare off. They give chase but Skye and Minimus keep trying to outdo each other to the point where they finally crash into a Highcliff Hawk nest. Sofia assures her friends it was not their fault. Chrysta appears and agrees by telling Sofia it is all her fault since she could not make a choice. Sofia decides to go with Skye which hurts Minimus' feelings to the point where he flies off. Sofia and Skye find the Mare and Sofia asks for one of her hairs. The Mare tells Sofia she knows who she is, but refuses to give her one since she only gives them to the true of heart. Sofia realizes what she means and goes off to find Minimus and apologize.
Meanwhile, Minimus gets stuck in a HighCliff Hawk nest. Sofia and Skye arrive and rescue him. Sofia apologizes to Minimus, and Minimus and Skye reconcile. They go back to the Mare, who gives Sofia one of her hairs this time for her WhichWay bow. Using the WhichWay bow, Sofia reunites with Chrysta. Sofia tells Chrysta that Minimus will be her Protector Steed in the Ever Realm and Skye will be her Protector Steed in the Mystic Isles. The group then heads home.