The Dark Knight Add-on for LEGO Batman 3: Beyond Gotham has 5 achievements.
Defeat Batman (Dark Knight Trilogy) as the Joker (Nurse) character
Complete the Dark Knight level with all Minikits unlocked
Set both Free Play characters as Bane (Dark Knight Rises) and Scarecrow (Batman Begins)
Complete the Dark Knight level
Complete the Dark Knight level after achieving True Hero status