Mordruuk is somewhere nearby

When Kagrokhan learned that Aldric's students not only survived, but were also trying to get into the sealed observatory, his rage knew no bounds. He could not allow the magic of the Abyss to break free.
In order to finally bury Aldric's legacy, the First Demon strengthened the observatory's defenses. To do this, he ordered the creation of the three-headed dog Mordruuk. The creature knew no mercy and fatigue. For centuries, it stood guard and attacked everyone who dared to approach the forbidden place.
Over time, the Abyss began to seep through the cracks in the seal that was placed on the observatory. And the first one it touched was Mordruuk. The magic ate into his mind, distorted his very essence. The Great Guardian ceased to be a servant of Kagrokhan, he began to obey the Abyss and left his post. Shamans tried to track him down, but the tracks were cut off, as if magic was hiding the fugitive.
Centuries have passed, but the demons remember this creature and fear that one day he will return. And his intentions will clearly be evil.