The Mr. X Nightmare Add-on for Streets of Rage 4 has 8 achievements.
Clear all stages in single-player mode as Estel.
Clear all stages in single-player mode as Shiva.
Clear all stages in single-player mode as Max.
Lead an army of 3 clowns.
Unlock all alternate moves for one character.
Unlock all alternate moves.
Reach level 18 in survival mode.
Reach level 30 in survival mode.