Kill more than 85% of the total enemies in a zone.
Finish a zone in less than 15 minutes.
Finish a zone without losing a life.
Finish a zone without using grenades or nukes.
Finish a zone killing less than 50% of the enemies.
Defeat the giant spider.
Max out all of the vehicle power-ups.
Don't waste more than 30% of your bullets.
Complete all underground zones.
Finish a zone in Co-op mode.
Finish a zone killing 60% of the units on foot.
Complete the game.
