Princess Star

Princess Star is a pony/Changeling hybrid that lives in the Changeling Kingdom, and she is 8 years old, and before the Changelings were reformed, Star looked like more like an alicorn, and lived in Canterlot with Princess Celestia and Princess Luna. It isn't visible in the picture, but Star has 2 scars on her left eye, that she got when defending a friend of her, that ended up at a Ursa Minor cave.
Her first friend was Twilight Sparkle, untill she met the rest of the Mane Six, and ended up being more friends with Rainbow Dash.
Personality
Star is emotionally volatile, and her mood can change really fast: she can go from shy and happy to agressive and angry in a flash, especially if Rainbow Dash is around the "Boy Bullies". She loves to study and communicate with her animal (and pony) friends. She can be a bit violent sometimes, but mostly, she's happy, likes to make her friends happy, and behaves like a princess while inside the castle walls and around Luna and Celestia.
Powers
Star can change shapes, just like a pony and a changeling. She can perform regular spells, as well as dark spells, since she inherited King Sombra's power and spells, such as Darkness Crystals, regenerating her horn instantly and making other ponies see their worst nightmare. Other spells she inherited were the hypnosis spell and consouming all the love from a pony or changeling, spells that she never used.
She created 2 spells: Healing and Portal, where she could open portals to any dimension, including Sonic the Hedgehog's world, where she became good friends with some of its residents.
Cutie Mark(s)
Princess Star has more than 1 cutie mark. The first one she got was a white star, that she got when she was 3 years old.
Her second one is a Red Fox. Just like Fluttershy, she got her Cutie Mark when helping animals calm down after Rainbow Dash performed a Sonic Rainboom. She then realized she had the ability to communicate with animals, and got her Cutie Mark.
Her third Cutie Mark is a black sword with a star pommel, surrounded by a red magic aura. Star was always fascinated by sword fighting, and one day, she sneaked into the Weapons Room and started playing with a sword, and ended up enjoying playing with it. She used to watch the guards train with the swords and kept visiting the same room every day, cpoying their movements untill eventually, she got her Cutie Mark. Star was afraid of what Celestia and Luna would think if they saw her Cutie Mark, and attempted to hide it for 3 weeks, but they ended up finding out about it. Fortunately, they weren't mad at her, and Celestia said it was a good sign: a Cutie Mark like hers could mean she was born to be a great princess, that would fight no matter what to protect its kingdom.
Her fourth Cutie Mark is a yellow star with a micophone in the center with the Eighth, Quarter and Beam notes above it. She got it while singing along "The Magic Inside", From Coloratura.
Element of Harmony
After Nightmare Moon's defeat, back when she was defeated by the Mane Six, Star read about a seventh Element of Harmony, the Omega Element, that was more powerful than the 6 elements together, and could be used as a substitute in case the 6 went missing. It could only be created if the 6 elements were put together, and a piece of each elemnt would be removed to form it. Star then followed the rules, and was able to create it. Twilight took Star back to the castle and explained the situation. Celestia then allowed Star to go on adventures with the Mane 6, seeing she could defend herself.
Discovering her past
After Queen Crysalis was defeated at the Canterlot Wedding, Star began to suspect she was also a changeling, but didn't have enough proof. Her suspicions got stronger after going to the Crystal Empire, where she felt really hungry for the Crystal Ponie's love. And, she discovered her suspicions were correct: Star wasn't just a Changeling. She was the Lost princess, a princess that was taken from her parents from a mysterious pony, and taken to Princess Celestia's castle, where she and Princess Luna took care of her. Then, she was divided: she didn't know if she would be evil like her parents, or continue to be good, and ended up choosing to be good. In the beggining, ponies were afraid of her, but they got used to it as time went on.
Pet
Star has a rather uncommon pet: a Night Fury named Night. Star adopted Night when the dragon was on a rampage, because Snips and Snails bothered her sleep, and Star was able  to calm her down. She then noticed Night didn't have a tail or left paw, and made both for her. It took 2 months, but Night trusted Star, and started living on an isolated area on the castle garden, and when Star moved to the Changeling Kingom after the Changelings were reformed, Night lived in a type of cave, that Star ordered the Changelings to build.
The My Little Pony Movie
Star was helping Twilight with the preparations to the Friendship Festival, but it was interrupted by the Storm King's Army and Tempest. The Mane 7 went after the Queen of the Hippos, who lived at Mount Aris.
On the way, they arrived in Kludgetown, where they met Capper, who tried to sell them.
While escaping from Tempest, the Mane 7 ended up on a ship of delivery birds, where they discovered was owned by what once was a pirate crew, and Star and Rainbow Dash motivated the pirates to ignore the Storm King's orders and be pirates again. Unfortunately, Rainbow Dash performed her Sonic Rainboom, and unfortunately, showing the Mane 7's location.
They had to evacuate the ship, and headed towards Mount Aris, where they discovered that the Hippogriffs abandoned the city. Pinkie Pie followed a sound, and the others went after her, and they were rescued by Princess Skystar, who showed her Seaquestria to the 7 ponies. Queen Novo transformed the 7 into merponies, and Spike into a pufferfish.
Twilight then suggested Pinkie and Star to "make Skystar and the merponies have some fun", but she tried to steal the magic pearl, but her plot was discovered. Queen Novo had no other choice but to ban them from Seaquestria. Back o land, the Mane 7 had a fight, and Star and Twilight got captured and sent to Ponyville to get their magic removed and given to the Storm King. Luckily, Star escaped and was able to warn the 5, along with Spike, that Twilight was captured, and were able to reunite with Capper and the pirates. And, to everyone's surprise, Skystar transformed back into a Hipogriff to help the ponies on land, but without Queen Novo knowing.
They headed to Canterlot, where Twilight and the princesses had their magic removed, and the ponies, including Star, fought bravely and got to Twilight, but it was too late. The Storm King betrayed Tempest, but Twilight and Star saved her. The Mane 7 reunited, and saved Equestria by working together getting the Storm King's staff containing the magic of the princesses. In the end, Tempest decided to take friendship lessons with the Mane 7, and the Friendship Festival was back on track.