Finish a zone in Co-op mode.
Finish a zone killing less than 50% of the enemies.
Finish a zone without using grenades or nukes.
Keep your accuracy higher than 70%.
Finish a zone killing 60% of the units on foot.
Complete the game.
Finish a zone without losing a life.
Finish a zone in less than 15 minutes.
Kill more than 85% of the total enemies in a zone.
Max out all of the vehicle power-ups.
Defeat the giant spider.
Complete all underground zones without using a continue.
