Unlockable Skill Challenge Puzzles
     Obtain  a certain number of stars to unlock these skill challenge
puzzles  which are timed random puzzles based on your skill level. You
earn stars based on how fast you finish the puzzles in Play mode.

Amateur:       Get 70 stars

Beginner:      Get 40 stars

Expert:        Get 300 stars

Mania:         Get 100 stars

Pro:           Get 230 stars

Rookie:        Get 30 stars

Semipro:       Get 180 stars

Specialist:    Get 450 stars

Sudoku Master: Get 650 stars

Veteran:       Get 130 stars