Dungeon Keeper 2 Walkthrough: Ambush/Silverstream: 9
This one is pretty easy - just 20 minutes, kill the Lord as he goes through. The trick is to prepare the way for him!
There are gems above your treasure room - go for them first, to get a steady stream of money. Also get a few more imps to help with taking over squares and with ferrying cannons.
Go SW first - this is pretty easy - as soon as you have four guys. Build a training room SW of your heart and train your guys up. Also build a prison SW of the hatchery to get skeletons from your victims.
Go NE to that guard room next, taking out both the top and bottom door, and the four cannons, replacing all of them with your own doors and cannons. Build 3 cannons around the middle guard room, and put a door at the top of it. Your aim is to trap the Lord in that middle room.
Now head SW to that last guard room and take them out. You should have about 5 minutes left. Make sure you have cannons along the path, but mostly get that middle room set and let your units train up.
When you hear the enemy has arrived, watch him move up the path. When he gets near that middle room, drop all of your units there. You should be able to kill him as he tries to break down the door to get out of the room. That's it!
Dungeon Keeper 2 Walkthough Index