Board Thread:Spoilers!/@comment-3010035-20150701044944/@comment-24674051-20150709165855

Or maybe it is a way of connecting all of the dark ones together, via the Dagger. The darkness has absorbed much from the different dark ones over the years, and perhaps through the connection with the dagger, the current dark one is able to pull on past memories from previous dark ones.

Because the darkness was absorbing the non-dark aspects, their appearances could show their Pre-Dark One persona (in which case, Rumple would be a peasant).