Timosa the Physician
You can defeat this opponent during the Mysterious Malady main quest. Once you have obtained medication for the Physician, you will have to return to your companions.
During the conversation you will have to make a choice, you can attack one of these characters – Magistrate or the Physician. If you choose the Physician, you will be able to kill one of the Ancient worshipers.
The fight against the Thamis will be harder due to her companions. Get rid of them and then kill your main target.