Baldur's Gate II: Enhanced Edition

Successful execution leads to obtaining the mage's stronghold, so it is better not to kill Valigar.
During the process, the name in the diary changes several times. Initially, “working for magicians in cassocks” (something like that), then “Hunting Valigar Cortala,” then “Planar Sphere.”
Before entering the sphere itself, we prepare thoroughly; the battles are not easy, and we won’t be able to get out before the end of the quest.
The trophy is awarded upon completion of the task, for the magician along with the stronghold.