What about... Gnomes fighting gnomes? like a 'battle gnome' as a skill and he'll kill all other colored gnomes as he comes to them. the other color can stop him by making another battle gnome and then the 2 will be stuck there fighting each other not being able to advance. You could work this into a more complex feature in the game... it would be an interesting take on the lemmings gameplay. but i'm just tossing out ideas.