Board Thread:Show-Related Questions and Answers/@comment-25926288-20151120003425/@comment-25926288-20151125194354

CoolDudeAl wrote: Back to the original topic, the DO can't cross realms because that is not one of the powers they have. Merlin and the Apprentice making magic doors may have been from a spell they found or created or something. And no DO ever knew and ever tried. But mostly, why would the DO not have that power if Merlin and the Apprentice does.

I know, I'm harping on the worldbuilding fail and the fact they didn't fully plan out the details, but at least they could go with "it's a super secret spell", but I guess not.