Project Mischief is the 10th and final mission in the A Fairy's Tale story line. You get this mission from Sylphie after finishing the Pint Sized Feast mission.
Hey, let's do this one last thing and I can reside here as your Fairy Ambassidor. Us Fairies, we do love our shenanigans!
"Keep those Garden Gnomes away from me! They get up to some crazy hijinx around 3 a.m."