The Gel'ziabar Hound is a powerful and territorial beast that can cross between dimensions. The monster appears when someone overuses the Gel'ziabar Stone's power. The Hound is massive, has sharp fangs and claws, and can leap great distances.
Gel'ziabar Stone Journal Entry
It seems to throw out a shockwave of considerable force, and ever since I acquired the stone I have noticed strange sightings and visual anomalies. However, the power of stone has its dark side. On occasion, a beast from beyond this world has attacked me. My only explanation for its appearance is that I was using the stone's power for too long. I have not seen the beast for a while, of course, I have not needed the stone...
Upon first arriving at the Covenant Manor, if Patrick looks back through the main gate, he will see a pack of Howlers run past being chased by the Gel'ziabar Hound. As the journal entry for the Gel'ziabar Stone suggests, if the active attack on the Stone is used too many times in the same area (without being interrupted by a loading screen), subsequent attacks have a chance of summoning a Gel'ziabar Hound which will immediately attack Patrick. This can happen anywhere, but many players go the entire game without realizing this. The Stone's non-damaging active attack is often ignored in favour of better attacks, and simply having the Stone in Patrick's hand to enhance his magical abilities is not enough to summon the Hound.
Later, during Patrick's battle with Ambrose Covenant, the villain steals the Gel'ziabar Stone, combines it with his axe, and transforms into a monstrous behemoth. The black sheep of the Covenant clan seems unstoppable, but suddenly, a Gel'ziabar Hound bursts from a dimensional rift. The combination of the stone and the axe's magics seems to have summoned the beast who attacks Ambrose, giving Patrick enough time to dislodge the stone from the weapon. Shortly after the battle, the hound reappears behind Patrick. He slowly turns around and the monster roars deeply. Patrick slowly backs away, but the Hound lunges at him, knocking him out.
The final scripted encounter with the Hound occurs in Oneiros. Count Otto Keisinger trapped one behind a magical barrier that blocks Patrick's path. Fighting the beast is entirely optional, and can be skipped at the cost of not collecting the useful upgrades kept in the room with the Hound. After using Dispel, the beast is most easily dealt with by attacking with Skull Storm and taking cover behind the small pavilion in the center of the room.