i read the pinned most common questions and i quote
Q: What’s this Purge thing?
A: The Purge is a PvE mechanic where groups of enemies will spawn in and attack players. As you play a Purge meter will fill up on your character screen, and once it’s filled you’re eligible for a Purge. Anything from human NPCs to beasts and monsters can attack you. The only way to make a Purge stop is to drive your enemies back or hold off their attack long enough until they retreat.
In general purges become more difficult the further north your base is on the map. Higher difficulty purges will contain special bosses with unique loot, or special crafter NPCs that have unique recipes on them. You will need a combination of smart base design, thrall defenders, higher tier buildings and good teamplay to withstand the most difficult purges.
I never bothered to check what the undead dragon had when testing purges, it must be insanely cool item noone has. anyone seen UNIQE loot? i know you can get keys from locust and scorpion for legendary chest, but this is not uniqe, wonder if i can discover something not know about if i test purges until i klled all the posible bosses, then i would have a new agenda since i already got all the tralls, ofc this must be done on official server to have any mentaly blingbling for me. anyone got anything on this Unique thingy or is it humbug.