Boreth

Boreth was once a normal person and a citizen of Carlin. He, his brothers Arthei, Marziel, and Lersatio, and Arthei's wife Kala, travelled to Yalahar in order to find a new home. From that moment on Marziel started keeping a diary.
Boreth is a plant-crazy vampire. You can see it by the lots of plants that grow in his tower. He is the first boss you will encounter during the Blood Brothers Quest. You can summon him by thrice using a Firebug on the Twines in front of his throne. There are 2 Plaguethrowers in his room.
You will receive The Dust of Boreth when you use a Blessed Wooden Stake on his dead body.

Fights until death in close combat. He uses Invisibility very often. Summons 3-4 Vampires at once.

Knights: the best option is to Exori or Exori Gran as much as possible while keeping an eye on your health. That way you kill all the summons as well so they don't do extra damage.