Board Thread:Show-Related Questions and Answers/@comment-25491743-20150817210639/@comment-25926288-20151226234137

DatNuttyKid wrote: Just because it could hold Rumple doesn't mean that it can hold the Darkness itself. From what Rumple said, the Darkness was gaining more and more power over him. So back in Season 3a, the Darkness wasn't as in control, so it could easily be said it wasn't as powerful either.

That could explain it, too - if the Hat and the Box are about equal in power (as is implied), but the Hat was designed specifically for Darkness removal but failed, then the Box probably couldn't do it either. It could hold it as in, Put the Darkness into a person and dump them in Pandora's box. Not a permanant fix, but if Rumple never left Pandora's box, you'd never have to hear from the DO again.

The Box doesn't remove the Darkness, but contains the vessel. Squid ink works on the Dark One as it does on any person and if the DO has the Darkness in them then you mobilized the threat. So, if you toss current Rumple in Pandora's box, he won't be able to escape and since he can't die the vault can't reforge him.