Smack the back of a mortar round of pavement, and you now have an impact grenade. Hang that under a drone, and you have a way to drop impact grenades on unsuspecting targets from an altitude high enough that the drone can’t be detected visually.

ISIS was doing just that a few years ago. There were/are plans floating around on the Internet for stabilizing fins for common mortar rounds - 3D print those, and you’re 90% of the way there.