Ozzrel is a very large, named alghoul. Kill him and take his head to the Royal huntsman to receive 200 
in addition to some experience points.
Spoiler warning: Significant plot details follow.
Ozzrel is found in the crypt in the outskirts, but only on a second visit having completed Buried Memories for Mikul.
Associated quest
Notes
- Talking to the Royal huntsman is not a necessary in order to unlock the secondary area of the crypt and gaining access to Ozzrel (i.e. you need only complete Buried Memories).
- Ozzrel can be a difficult foe, but he does turn his back which is a good time to strike.
- Using potions and oil can also help defeat him more quickly.
Significant plot details end here.