When you begin the mission to search for the Green Minions, you will have to 
sneak into a castle using your Minions. While you are in there, you will 
discover a few pressure plates that release gnomes as a distraction to the 
enemies. However, as long as there are still enemies in the castle the gnomes 
will keep spawning. This allows you to not only get the 1,000 kills of a gnome 
quickly, you will also be collecting crystals, gold, and Lifeforce orbs while 
doing so.