The Keystone fragment fuses with the Improbability Drive, granting you the incredible ability to manipulate dissonant reality and, by extension nexus. This allows you to manipulate the other place to an extent, allowing you to create portals between realities, create beams that destroy your targets on a molecular level, switch your consciousness between various host bodies, manipulate reality on a global scale, and drag people into "Hell" or The Other Place.
While in "Hell" (or, to a lesser extent, The Other Place), you are capable of creating and destroying life, reshaping the laws of reality, and fundamentally rewriting power systems with the exception of your own. These changes will remain to beings that you send into the real world, such as your duplicates, whom you may still edit and possess.
Slowly reality will stop rejecting your changes and With enough time, you could reshape entire solar systems into paradises or send them and their people screaming into "Hell".