Complex sentence: Empress Gravelyn, leader of Evil, informs you that Lionfang has kidnapped all the major heroes (Artix, Galanoth, Cysero, etc.) and has renamed his Thunderforge base to "Onslaught Tower," which was an event in the beginning of the game.
Split into simpler sentences: Empress Gravelyn, leader of Evil, informs you that all the major heroes (Artix, Galanoth, Cysero, etc.) have disappeared. Lionfang had renamed his Thunderforge base to "Onslaught Tower," which was an event in the beginning of the game.