Ghostopolis by Doug TenNapel

When world-weary ghost wrangler Frank Gallows accidentally zaps terminally ill Garth Hale into the in-between dimension of Ghostopolis, the boy finds himself with a new lease on life—or death, as the case may be. As a human being in this spirit world, Garth discovers he has incredible powers that are capable of overthrowing Master Vaugner, [...]