Invisible Sun: The Nightside - Rules of Play says:
The Nightside is your guide to this dangerous antithesis of the Path of Suns. Some who call upon this forbidden tome will undoubtedly be seen as villains, but though its use is risky, it is not inherently without benefit. If you are willing to accept that risk, you will find new fortes, new patrons, dozens of magical practices—minor and long-form—and Nightside locations and characters. And, of course, many secrets of the Nightside. This product contains:
- The Nightside, a 192-page book, enclosed in a special warded bag to protect the other tomes in your library from its dark and unpredictable effects.
- 40 Nightside magic cards, including spell, incantation, aggregate, ephemera, and object of power cards, plus 10 new Vance spell cards.
- A unique experimental die, unlike the mundane or magic dice in the Black Cube, for use with Nightside magic.