"Gnome Grinder", "Minion Hoarder", "Minion Lover" achievements hint
When starting the mission to search for the Green Minions, you must sneak into a castle using your Minions. While you are in there, you will discover a couple 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 continue to spawn. This allows you to not only get the 1,000 kills of a gnome quickly, but you will also be collecting crystals, gold, and Lifeforce orbs while doing so.