Even for one such as Lilly, there isn't enough time to do everything she wants. She has duplication spells, conjuring copies of herself, but they can only stretch so far, only lasting while she's awake. So she was thrilled when she got the Orb of Umbral. It has the power to bring one's shadow to life. However, it can only bring one shadow to life at a time.
She has dubbed this clone Dark Lilly. She's an almost perfect copy, but with a few differences. While Lilly's main affinity is for light magic, Dark Lilly has an affinity for shadow magic, although she is still capable of light and the other elements, shadow has become among her highest affinities. She is also capable of hiding in shadows with ease. However, the Orb of Umbral also twists the personality of the clone, resulting in her being less sadistic then the original. The change is consistent, at least.
Dark Lilly possesses all of the original Lilly's memories... such as they are. When they merge up or when Dark Lilly is dispersed, they sync up and Lilly learns everything Dark Lilly learned. Only after this can a new clone be created. While the orb can only create one clone at a time, unable to even bring someone else's shadow to life, Lilly has managed to develop her armor in such a way that it will be copied as well, even its mana well, provided she's wearing it at the time.
Dark Lilly is a useful double, able to help with experiments and management, acting largely how Lilly would act. The notable difference between the two of them is that Dark Lilly wears black clothes. The two of them can conduct different experiments, even working on continents at the same time.