Marina Mistfire is the main protagonist in VoicesFromTheDark's series, The Champion of Cyrodiil Challenge. Marina is a Breton battlemage who often has funny quirks, and is incredibly fast. But, the best way to explain The Champion of Cyrodiil Challenge, is what is written in the video description by Carl himself.
"In this let's play/walkthrough of The Elder Scrolls IV: Oblivion, I intend to get 100% game completion while playing on the hardest difficulty. I will do every quest, clear every dungeon and master all skills. I have made a custom set of rules for this challenge which will make the task more daunting, and I will avoid abusing powerful exploits. My character is a Breton battlemage named Marina Mistfire. Note that I am not planning on including the Shivering Isles & Knights of the Nine DLC into the challenge as of now. The same goes for the other official addons released by Bethesda, like Frostcrag Spire and Thieves Den. I have the Shivering Isles installed and activated, but that's just to avoid issues with missing textures in the Niben Bay. The main focus right now is on vanilla Oblivion, and that has to be completed 100% before I do any addons."