Complex sentence: When the heroes tracked the Dragon to his new stronghold, the Dragon had them surrounded by his minions, but Iowerth convinced them to reject the Dragon's influence, the Dragon then manifested in the open and attacked Iowerth.
Split into simpler sentences: When the heroes tracked the Dragon to his new stronghold, the Dragon had them surrounded by his minions, but Iowerth convinced them to reject the Dragon's influence. The Dragon then manifested in the open and attacked Iowerth.