In the midst of the Void, Mark meets the uncorrupted consciousness of the Dream God. That consciousness offers him his Legacy, free from the Control of the Main corrupted body.
But something -Unknown- in Void forces him on a much larger Path that Suppresses All, even the True Gods.
And this -Unknown- being gives him the privilege because of only one thing. Mark doesn't have a limit on how strong he can be. He can suppress Transcendent beings while still being a Dreamer.
And this Limitless Potential is granted to him by a almost dying System, which is going to become one with its last Host.