Oona

Princess Oona is a character in the Sofia the First special Sofia the First: The Floating Palace. She is a mermaid who befriends Sofia. When she gets kidnapped by a sea monster, Sofia, with the help of Cora, goes to save her.

Background
Oona first meets Sofia when she comes to the surface to take a closer look at the Floating Palace. She accidently gets caught in a net until Sofia untangles her. The two of them soon become friends, and after Sofia's amulet gives her the power to become a mermaid, they dive into the ocean together.

Oona takes Sofia to her hideaway where they meet Sven and her older sister Cora who treats her like a "mer-baby."

Trivia

 * Oona becomes the first and only other princess to learn and witness the magic of Sofia's Amulet.
 * Like Sofia and her amulet, Oona wears a magical comb which gives her the power to control waves, making her the second princess in the series to possess a magical object.
 * Even though she has the magical comb, Oona isn't shown yet how to use its power. In fact, she never uses it. This makes her more of a vessel than a wielder so far in the franchise, which is further supported by the fact that the comb has a spell on it that prevents anyone from physically taking it from her.
 * Like Ariel, Oona can not only talk to sea creatures but also to land animals.
 * Like Ariel's Secret Grotto, Oona has a secret hideaway that is a sunken shipwreck, where she keeps all her treasures.
 * Oona shares the same name with the mermaid character from Nick Jr's Bubble Guppies.
 * In many ways, Oona is very similar to Sofia: Both are the youngest princess of a kingdom and both are given a mystical object that contains magical powers, both received these from one of their parents. Both also have older sisters.
 * There are also differences between Oona and Sofia as well: Oona's only family are her mother and her older sister while Sofia has a father and a older brother. Sofia is able to use two of the powers that her amulet gives her, but Oona can't use the powers her comb gives her at all. Oona was born a princess and Sofia became a princess after her mother married the king.
 * Oona received her comb from her mother who is aware of it's full potential while Sofia received her amulet from her father who doesn't even know that it's enchanted.