Board Thread:Character Discussion/@comment-26340222-20151020185228/@comment-24674051-20151021154630

As far as we know, Excalibur is the other half of the Dark One's Dagger. so it is not JUST a Sword. Now, whether it has any additional magical properties remains to be seen, but I would seriously doubt that the most legendary of swords in any realm (even ours) would be "just a sword". Just saying.

As for who put the sword back in the stone, That is a good question, and I have not seen anything that forshadows that event. My best guess at this point is, based on what we've seen, would be Robin and/or Belle. And, in all honesty, shoving the sword back into the stone seems like such a Belle thing to do.