Change into a costume.

Defeat Queen Leech.

Obtain all keys and use them all.

Defeat the Proto Tyrant.

Fight off the Proto Tyrant.

Use a Green Chemical.

Defeat Infected Bat.

Complete the training facility.

Defeat an enemy with a critical-hit headshot.

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

Defeat Centurion.

Complete the train.

Defeat an enemy with a knife.