Board Thread:General Discussion/@comment-7503158-20160205001637/@comment-25660412-20160308065034

Vilgax was trying to retrieve the chromastone crystal because it was stolen from him and the crystal had a lot of power (enough to destroy a diamond hard world).

He freed Zs'Skayr because he wanted the secrets of the Omnitrix and only Zs'Skayr knew those(He was the only one willing to talk)