Challenge Points

Challenge Points
Challenge Points (Chp) are a resource gained by completing challenges. They can be used to buy various bonuses. As of July 2021, around 23,000 CHP are available.

Good early purchases are damage reduction vs UBs, pet xp overflow, auto half stats and crystal upgrade boost. A few levels in adventurer XP boost can also be helpful. After these purchases, the rest depends on your own playstyle and what you feel would benefit you the most.