Here's how to defeat the Zombiebot king. You have to keep shooting him until he stoppes moving. The scatter blaster and cleaners are effective. Once he stoppes moving you have to throw corrosive charges into his mouth, which will be open. It may seem difficult to get the grenades in at a distance. What I found most easiest and effective is walking right under him and looking up and throwing them in from underneath. Do this 4 or 5 times. Simple.
This works best on the drill level on multiplayer.Get a friend to get in a sentinal and get on top of him tether somthing while still on it and tell your friend to go to the top of the drill and exit your bot and you will be on top of your friend and will be able to snipe from the drill.
In the ''You Know The Drill'' level, tether the Predator. Then pick up a secret chip. Look at the mission objective in the pause menu for a note from one of the level designers.
To unlock the original concept movie, finish the whole Campaign (Story) mode.