Board Thread:General Discussion/@comment-31512959-20161223050356/@comment-24674051-20161223173322

The show has not made it clear...yet. Now, they may or may not make it clear at some point, but I hope that we have not seen the last of Nemo, Liam, or the Nautilus.

Now, as for the the realm-crossing ability, I agree that it does seem likely that the sub has somehow acquired this ability. Maybe is has harnessed mermaid magic, maybe it was build by merpeople. Maybe there is another reason we don't know yet.