Completing this mission on any difficulty unlocks Joker and Ketch as Private Army Operators for use in the Zombies mode, and completing it on Nightmare difficulty unlocks their personal weapons Terminal Velocity and Kohhn as Loadout weapons in Zombie Operations.
Underground - Complete "Underground" on any difficulty.
Sewer Rats - Complete "Underground" on Nightmare difficulty.
Thanks, Agent! - In the underground levels, do not allow a single Mirage Security Trooper or Police Officer to die on Nightmare difficulty.
Weapon Specialist VI - Get a kill with every obtainable weapon on Nightmare difficulty.
Ancient Relic VI - Find the pristine AK-12 in the Security Locker.
Trivia[]
Obtaining the "Weapon Specialist VI" achievement/trophy may be difficult as the DC-15A, ICR-7 and Strife are only dropped by the Mirage Security Trooper and Police Officer NPCs.
This makes obtaining all achievements/trophies on this mission requiring two playthroughs.