Cadderly uses Catti-brie as a conduit to enter the Shadowfell to finish off the Ghost King. In the end, Cadderly defeats the Ghost King at the cost of his life and becomes the new Ghost King, forever reinforcing and guarding the ward containing the rift left by the old Ghost King.
Cadderly employs Catti-brie as a medium to gain access to the Shadowfell in order to eliminate the Ghost King. Ultimately, Cadderly triumphs over the Ghost King at the expense of his own life and assumes the role of the new Ghost King, thus solidifying and safeguarding the barrier created by the previous Ghost King.