A low threat monster / master. Maybe a side plot that distracts from main session plot or eats up time and complicates things. Or the origin of your big bad….
http://randis.deviantart.com/art/GOLEM-toys-and-magic-136349010
http://randis.deviantart.com/art/GOLEM-toys-and-magic-136349010
How fun! The PCs get approached by the kids whose shenanigans have resulted in some neighborhood chaos?
Bonus points for linking to the source.