A group that wished to be 'ever-living' instead was cursed with 'never-dying'. Thier flesh rotted and fell fromthier bones but still they lived on. Now as skeletons they continue thier quest to remove thier curse. As skeletons they differ in that they do not need controlled or summoned. They are fully fledged NPCs with drives or ideas of thier own. Stabbing and slashing weapons would not affect them.
Shadows, Mirrors and Flames. Three things we have all seen and not given much thought to. What if in each of these things you could find entire alternate planes of existance? Shadows move but what they are shadowing does not. Mirrors show us what others can easily see. Flames dance and twirl inviting you to dance only to scorch you when you get close. These three things hold much mystery. What if you could harness their powers? Heh...