Arendelle Legend Trilogy 

The Master, Lord Shen (Iblis)

Long ago, in ancient China, the Peacocks ruled over Gongmen City. They brought great joy and prosperity to the city, for they had invented fireworks. But their son, Lord Shen, saw darker power in the fireworks. What had brought color and joy could also bring darkness and destruction. Shen's troubled parents consulted a soothsayer. She fortold that if Shen continued down this dark path, he would be defeated by a warrior of black and white (a panda). The young lord set out to change his fate, but what he did next (destroy almost all the panda population) only sealed it. Shen returned to his parents full of pride, but in their faces, he saw only horror. He was banished from the city forever, but Shen swore revenge. Someday he would return, and all of China would bow at his feet.
Of course, this would have been true if Master Po and the Furious Five (Masters Monkey, Crane, Mantis, Viper, and Tigress) hadn't defeated him in the Hong Kong Harbor. But unbeknown to them, he was not dead. He was very seriously injured, though. Some molten metal got into his injured parts, and he was healed. He then walked to Mt. St. Helens, jumped in, and immediately became the Flames of Disaster known as Iblis. Then he created minions called the Black Arms with their appointed leader, Black Doom (one of the creators for Shadow).

In 1814, he attacked the mystical forest right next to Arendelle, but the forces of light fought against them and ultimately won against them. Koragg was then formed when Leanbow trapped him inside the Pit, where he resided as his form of Iblis.

Now in his form as the Master, which Iblis is now called, he became the raw power of the sun god Solaris and an immortal energy-based being of mass destruction. Iblis was said to be born, according to the first appendix in the archives of Arendelle (because the kingdoms of Soleana and Arendelle were very similar in many ways, and because Sonic was able to tell Anna and Elsa), during the Solaris Project when the experimentations on Solaris split him into Iblis and Mephiles the Dark. Following its birth, Iblis was sealed inside the soul of Princess Elise by the Duke of Soleanna.

Ten years later, Iblis was targeted by Dr. Eggman, who sought its power for world domination. In the main timeline, Iblis was released and ravaged the world far into the future. However, this future was averted thanks to Silver, Sonic and Blaze. Regardless, Iblis was still released by Mephiles and the two rejoined and remade Solaris, only to be defeated by Sonic, Shadow and Silver, and subsequently erased from existence, or so it seemed.
When Sonic returned to Arendelle with many friends, an earthquake struck, which allowed the Master to begin terrorizing the place once again and destroy the world (once he was killed and reborn, he did not just want to take over China, but the whole world). Black Doom, his assistant, then sent out the people of the mystical forest. But once he was defeated, the Master not only lost his Black Arms and his assistant, but also Koragg, his most loyal servant. So he decided to have Dr. Eggman help him out, and it worked out a little bit. Eggman's robots already had gone bezerk once the earthquake struck, so they were programed to follow the Master's ways. The Mystic Rangers then came and found out that he had already upgraded Metal Sonic for his final form. At last, they arrived at the secret laboratory, where he killed Sonic and sent him into another location. The power of the other Rangers were significantly limited to almost having no power at all. He captured them and took them into one of his flying ships that Eggman had built for him, but Sonic came back. This then caused him to transform himself into the final form with a rock monster named Tai Lung, a water monster similar to Perfect Chaos, Reverse Flash, and the Wind Master. Together, these four monsters merged with Shen and Metal Sonic, and Lyric was formed. Sonic's friends then came and tried to defeat it, and they were all knocked out. However, Sonic, Shadow, Knuckles, Amy, and Blaze turned into their Legend Warrior mode with the help of Udonna, Leanbow, and Silver, and they were able to destroy the final form. Finally, Eggman and Metal Sonic had had enough. They decided to turn over a new leaf, but the Master, being reluctant, fought Sonic, who ultimately destroyed him for good. And nobody knows if the Master is being reborn to this day, but it is very unlikely.