Complete level 1 - The Downfall Bridge
Complete level 2 - Ruined Factory.
Complete level 3 - Down in the Pit.
Complete level 4 - Metro Station.
Complete level 5 - Bottom of the Sea.
Complete level 6 - Dead Ships.
Complete all challenges on level 1 - The Downfall Bridge
Complete all challenges on level 2 - Ruined Factory.
Complete all challenges on level 3 - Down in the Pit.
Complete all challenges on level 4 - Metro Station.
Complete all challenges on level 5 - Bottom of the Sea.
Complete all challenges on level 6 - Dead Ships.