|Halflight, Spear of the Church|
If playing online, a player in Spears of the Church can be summoned by the adjudicator as a boss.
Using the pillars around the room allow you attack and hide quickly. Kill any Painted Guardians as fast as possible, if they are kept alive they will heal the boss.
An attempt on youtube that may help: https://youtu.be/wcnidvWvbeM