The Your Best Nightmare Add-on for Groove Coaster has 6 achievements.
Play Your Best Nightmare 20 times
Play Your Best Nightmare and clear all of SIMPLE, NORMAL and HARD
Play Your Best Nightmare and get A Rank in SIMPLE, NORMAL and HARD
Play Your Best Nightmare and get S Rank in SIMPLE, NORMAL and HARD
Play Your Best Nightmare and get S+ Rank in SIMPLE, NORMAL and HARD
Play Your Best Nightmare and get S++ Rank in SIMPLE, NORMAL and HARD