Hidden bonuses: 3
Level walkthrough: Turn left the second you've started this level and go through a large hole in the wall to find the first bonus item. Proceed to the main tunnel and it won't take long before you're attacked by a stronger version of a Biomech.
Notice that this new mech is much more agile than the machines you've been encountering so far. You'll also have to avoid its new attacks, including a leap attack. Don't get too close to the mech or otherwise it'll use a heavy weapon to kill you with two shots. There are two ways for you to get rid of the mech - you can start using heavy weapons yourself or you can keep throwing objects at it. Don't forget to retreat to safety each time you've suffered a few hits.
Head forward after you've defeated the mech. It shouldn't take you too long to find an area with the second bonus item. Attach yourself to the ceiling and reel yourself in to take this object. Proceed to the next section which is being occupied by enemy troops. Choose grenades or a grenade launcher before you get close enough for them to see you.
Try eliminating larger groups at the same time and prevent enemy soldiers from surrounding Spencer. Be on a look out for more supplies as you advance towards enemy positions. You should also consider throwing nearby objects at enemy troops.
You'll have to deal with three more groups. Don't forget to move back to a safe area if Spencer is about to die, because otherwise you'll have to start over from the last checkpoint. The final third bonus item can be found behind the bus. Take the object and move to the tunnel on your right to leave this area.