Once Upon A Time Season 8

Lost City: Back to the surface

Emma and the other heroes had to figure out a way back up, when King Milo offered a way to fix the Nautillus using Atlantean technology, which was powered by magic. Getting a piece of the cristal that powered Atlantis to get the submarine back on track. he took them to the stone while he told them the story of Atlantis.

A long time ago Atlantis

The city of Atlantis was large and flourishing city with visitors coming from all over the world to see its amazing organization and magic based technology, young princess Kida couldn't have asked for a better home, she loved playing with the ships and controls.

Suddenly the heart to the city started glowing and some yellow smoke seemed to surrounding the city, her mother reached for the heart and she started floating as the heart absorbed her then a pulse of energy came from the heart it seemed to cover the center of the city like a bubble that was sinking into the water away from the yellow smoke, from the rest of the world.
1910
The isolated atlanteans knew nothing of the out side world after centuries of hiding they didn't know how long it had been when a giant ship crashed into the entrance caves, a group of people appeared, outsiders, even if they looked quite different to the ones that they remembered. One of them stood out to the princess, he used some weird accessory on his eyes and carried a book with him why did it take so long for outsiders to come back?
Milo and the outsiders told her how much the world has changed how he knew about their city as a legend, but he knew nothing of magic, apparently the outside world had forgotten it, and in all fairness the atlanteans had as well, except for the necklaces that kept them young and alive.
They wanted to find the secrets long forgotten by the people, either for research or personal gain, Milo came to understand the city and helped them recover their past, and he did and he stayed.

Present Day

The Nautilus was nearly fixed.

Are you sure this is going to work? you know magic doesn't exactly work in this world or not very well. Emma said.

It will work mom, this magic belongs to this world according to what Milo told us, it should work perfectly, and we can use it for our purposes, and we could bring them back to the surface once all of this is over and we bring back belief. said Henry

We need to be careful Morgane could use this magic against us. Said Mulan who was with Shang who was still confused.

Some hours later

ok we're almost there. Said Graham

suddenly a Black smoke twirl appeared in the middle of the submarine and from it appeared Morgane

-You thought you could go outside and me not knowing about it, just because I let your friends go doesn't mean I stopped watching you. I wanted to know what was it that you found. Vestigial magic from this world, enough to power your submarine. how much of this could help me to complete my mother's work? she said

-sorry but you're out of luck, this is protective magic not destructive magic it is useless to you. Henry said.

-well my mother could corrupt her happy flower magic, I'll find a way to corrupt your "protective" magic I just need a coven, amongst all the realms in this place sure there are enough witches