Complex sentence: Merlock makes his next appearance in the video game "Legend of Illusion Starring Mickey Mouse", in which he is known as the Sorcerer of Darkness and is responsible for stopping the River of Time and threatening the Tree of Life in the process.
Split into simpler sentences: Merlock makes his next appearance in the video game "Legend of Illusion Starring Mickey Mouse". Now known as the Sorcerer of Darkness, he is responsible for stopping the River of Time, threatening the Tree of Life in the process.