How to get the powerful undead fragments of DNF? What's the use?

DNF's tough undead fragments were obtained by hitting the Lord's tower. The monster falls off and cannot be traded.

The key to changing the fate of the mission is to collect 25 difficult pieces of the undead. You can get the undead treasure chest after completing the task, and you can get the undead crystal by opening the undead treasure chest.

Undead shards, you can exchange ten shards for a crystal, accumulate a certain number of crystals, and buy SS equipment.