There are many stories of warlocks and witches using their shadows to do nefarious things. Using them as spies, to attack another persons shadow causing the victim physical harm, using them as something akin to a familiar, or the shadow even a physical manifesting into an agent of their vengeance. So how would a wizard accomplish this without a mystery? To me, it does not seem to be something that should be outside of the hermetic purview. It doesn't break any of the limitations so far as I can tell. But what would the form be?
Lightness Agent of Vengeance
ReIg (Mu Pe Me) 25
R: Touch T: Ind D: Sun
Detaches and turns a persons shadow into a lightless agent of the caster able to effect the physical world around it. The shadow is nearly mindless and can follow verbal and mental commands of the caster. This spell was created as a weapon by a Predo Flambeau to use in wizards wars as the shadow can slip between cracks and reach out to strike a target, though other wizards have found utility in having their shadow as a servant. The shadow cannot exist in lightless rooms and takes double physical damage from any fire based attack, but is otherwise very difficult to damage unless caught interacting with the physical world which makes parts of it wholly physical. While active the caster has no shadow and if destroyed will remain shadowless until the duration ends.
(Base: 10 wholly unnatural, +1 Touch, +2 Sun)
Here are my thoughts. Creating light is Creo Ignem, absence of light is Predo Ignem. So one way to manipulate manipulate a shadow would be Muto and Predo, primarily being rego to control function of the shadow itself. Thoughts?