Do tu think the legendarium can unlock with the legendarium key? When the legendarium can lock, so must can unlock? What do tu think?

The Legendarium Key was sealed forever with the legendarium. So the legendarium key can't unlock due to the fact that the key only locks the legendarium FOREVER. Hope this helps you!

The Legendarium key may possibly be able to unlock the Legendarium. But tu can't blast it open that's for sure. Maybe tu could also destroy it. But maybe, just maybe, the key can unlock the Legendarium as locked it before at the end of season 6. So, maybe.

Well, it would be kind of boring if the Trix were in there forever, so I'm sure there must be some way to open it.