When Sionaas put out the call for workers to construct a basement below his tower, many workers came to earn some coin. He also called upon a band of heroes, telling them that there was an orb below his tower that could reveal the location of a great treasure, and he would cut them a share if they found it. In reality, his tower was built upon the ancient remains of a temple of Lolth, and the orb was in fact one of the keys to the drows' prison. The heroes discovered this, however, and fled with the orb, successfully keeping it safe from Sionaas's reach. A few months later, when one of the heroes, Tol Sigurn, left to spend some time with his friend Torgar, he was ambushed and captured by Sionaas. Torgar rallied the other heroes, who invaded his tower and forced him to assume his true form. After a fierce battle on the tower roof, Torgar swung his axe and severed the dragon's head, leaving his body to topple down to the bottom. Tol was found battered but alive, having been tortured for information by the wizard.
Sionaas's skull subsequently hung in Leardon Sunflare's laboratory within Brightstone Keep for several years before being moved to his palace in Terastra. It has been enchanted with warding spells to attack intruders with magic.