Byzzr Wingmender is a Mantismonkboss. Though he may appear alone to start with, once you approach him, a large group of Mantises will drop down to join him.
Probably the best way to take Byzzr down is to have everyone in your party use nothing but ranged skills, thus not activating his patrol: that way, he'll be alone, and should die rather quickly.
Henchmen attacking Byzzr will not set off the patrol either, only players.
Players can hide behind the rock and use it as a barrier from Byzzr's attacks and use non-projectile spells.