Surprise your players with unexpected attacks. Gnomes, who are generally friendly are starting to attack. Why are local gnomes on the offensive? What is that strange light in their eyes? Did that one just hit me? What’s going on? Drop this side trek into your current dungeon crawl on a night when your players are least expecting it, or when they’ve gone around the wrong corner, and you aren’t ready for them to go that direction yet.
Enough adventure for an evening or two for 1st-2nd level characters