How to complete the Hidden Task?
Wandering in this floor and you can see a “Magic Stone” on the ground, collect it
How to finish the hidden task on the 10th floor?
Click to open the map, you can see a Portal in the center, beat the doorkeeper then enter the portal to go to another place.
You can find a shinny stone, pick it up, and beat the Black Dragon. Aftet that you can finish the hidden task.