Hidden bonuses: 3
Level walkthrough: Ignore new skyscrapers located near your position. Move forward and jump into the abyss. Wait for Spencer to reach the ground floor and you should notice that you've ended up inside a partially destroyed tunnel. Thankfully there aren't any enemy units nearby. Head forward and stop upon your arrival in a much bigger area.
A huge walker will appear above the canyon and it's going to start sending out smaller drones to hunt you down. I would strongly recommend that you get to a nearby pod as soon as possible, because it contains a machine gun. This weapon is by far the best choice when fighting the drones, so make the exchange when you get to the pod.
Use your newly acquired weapon to get rid of about a dozen of drones and the rest should leave you alone. Instead you'll notice that enemy paratroopers have landed inside the cave. Ignore them for the time being and focus on getting to the first bonus item. In order to do that you must swing a few times while being attached to the closest ledge.
The second bonus item can be found on an upper ledge, located to the left of the exit from the tunnel. It shouldn't take you too long to find it. Once you have it you may finally focus on getting rid of enemy soldiers. Throw objects at them or use the machine gun if you have spare ammunition.
The final third bonus item is safely hidden on a lower ledge, so you should climb to an upper platform to locate it. Take the object and proceed towards the designated area of the map. Take ammunition and approach the blue gate. Go to other side.
Get ready to defend yourself against a new upgraded Biomech. Make sure to use rocks from your vicinity to damage the mech. You should also consider staying on an upper ledge, because the mech may have problems reaching your position, so it's going to be an easy target. Keep attacking the mech until it's destroyed.
You may proceed to the next section. Make sure to watch a new tutorial movie along the way, because you'll want to test your new move on some of the nearby enemy soldiers. Remember to keep completing challenges as you go. Once it's safe proceed to a new tunnel which will lead you to the exit.