Obtain all keys and use them all.

Complete the factory.

Complete the laboratory.

Defeat a zombie by stomping on them.

Get picked up by the Infected Bat.

Create a Custom Handgun.

Shoot down a Hunter or an Eliminator while they are jump attacking in the air.

Defeat Centurion.

Defeat an enemy with a critical-hit headshot.

Change into a costume.

Attack an enemy to save your partner who is grappling with that enemy.

Complete the entire game on Amateur.