Complete single player mode to unlock New Game + mode. You will retain your previously unlocked weapons and upgrades, as well as unused Grey Tech cubes you have found.
Superhuman difficulty:
Complete single player mode to unlock the Superhuman difficulty.
Trophies:
Bronze trophies
Staten Island - Successfully complete level 1.
Military Ocean Terminal - Successfully complete level 2.
George Washington Bridge - Successfully complete level 3.
Ellis Island - Successfully complete level 4.
Protection Camp - Successfully complete level 5.
Conversion Tower - Successfully complete level 6.
Upgrade - Upgrade a weapon in the Single Player Campaign.
Indiscriminate - Kill an enemy with every weapon in the Single Player Campaign.
Variety - Use the secondary fire of each weapon in the Single Player Campaign.
Dangerous - Kill 250 Chimera in the Single Player Campaign.
Silver trophies
Combine - Upgrade both slots of a weapon in the Single Player Campaign.
Deadly - Kill 500 Chimera in the Single Player Campaign.
Axed - Kill 50 Chimera with Riley's axe in the Single Player Campaign.
Overheat - Kill 50 Chimera by detonating their heatstacks in the Single Player Campaign.
Boom - Kill 100 Chimera with headshots in the Single Player Campaign.
Impaled - Kill an Impaler.
Executed - Kill an Executioner.
Gold trophies
Customize - Upgrade all weapons in the Single Player Campaign.
Lethal - Kill 1000 Chimera in the Single Player Campaign.
Giant - Kill any combination of 18 Impalers or Executioners.
Incite - Complete one round of multiplayer.
G-man - Kill Gorrell.
Unnatural - Kill the Abomination.
Inhuman - Kill the Leviathan.
Platium trophy
Platinum - Earn all Bronze, Silver, and Gold trophies.
