The Dark Mirror of his Dreams Sandy, the Sandman gives the king of doom a mirror to put his visions so he can scry them and not experience them like his uncle, he tries til the mirror cracks what terrors can come out of the mind of doom.

Also in book

Once in a Blue Midnight There were whispers that the reaper king Mortimer once lost his human form, his body, his shell. Among the reapers, rumors changed it to his soul being stolen.

This is what really happened...