When I redesigned Johnathon Louck's Illuminate mechanic from his GDS2 submission, I felt I had a workable version that gave the light side a character. So Light = Illuminate, Dark = Morph. I wanted to suggest a mechanic that could be shared by both sides to add tension and conflict. Then, I remembered Shadow. Shadow was perfect to return to Johnathan's setting, you need Light and Dark to make shadows and it could be easily themesd to either side. Dark hides in the shadows and sneaks around. Light defends the shadows, seeking to sweep them away along with everything else dark. This was my first Shadow design.