We do not have official information about how the spawn works, but by observation that I could do in the test server and in lasts 3 days, the spawn of the creatures are random (when you kill a creature, it can spawn a Usurper Archer
, Usurper Knight
or Usurper Warlock
), like the spawn of the Glooth Bandits and Glooth Brigands
.
So, if you need take Broken Longbows
, the best tactic is kill all Usurpers.