Umbrakinesis, also known as Dark Magic, is a dark and corrupt form of Sorcery. It grants the wielder the ability to create, control and manipulate shadows and darkness. Shadow spies are a form of Umbrakinesis.
Shadow Weaver was the most notable wielder of Umbrakinesis, which she was imbued with by the Spell of Obtainment. She enhanced this magic through her artificial connection with the Black Garnet and occasionally combined it with Electrokinesis. She regularly used it to abuse and intimidate Catra, often forming black tendrils with it. However, after Shadow Weaver's connection to the Black Garnet was cut by Catra she appeared to have lost her ability to use Umbrakinesis. She later recovered it by accessing Glimmer's connection to the Moonstone and absorbing some of the magic from the Heart of Etheria.
After being chipped and placed under the control of Horde Prime, Micah began using this magic to great and terrifying effect, at one point using it to manipulate his own shadow to form black tendrils, and even using it to immobilize almost all the Elemental princesses with a single spell. He also used it to combat Glimmer, using it to shoot bolts of dark energy and at one point creating a massive swirl of darkness, but was ultimately defeated by his daughter. Micah presumably stopped using Umbrakinesis after being freed from Horde Prime's control.