Complete the indicated task to unlock the corresponding type of challenge at the "Challenge" menu.

Easy Boss challenges: Reach the boss under Easy difficulty.
Easy Mini Boss challenges: Reach the Mini Boss under Easy or Normal difficulty.
Hard Boss challenges: Reach the Boss under Hard difficulty.
Hard Mini Boss challenges: Reach the Mini Boss under Hard difficulty.
Normal Boss challenges: Reach the Boss under Normal difficulty.
Normal Mini Boss challenges: Reach the Mini Boss under Normal difficulty.