Beware of spoilers below!

Interdimensional portals
There are gates that randomly appear in the middle of the ocean here and there, which take you to the Ocean of Time. It’s a seemingly infinite body of water, where you can travel to other worlds through these randomly appearing gates.
If you know some strong kind of magic, you can create such a gate yourself, and even set the point of destination.

When Willie finds herself on the Ocean of Time, she meets an inexplicable ghost who helps her out(?).
Erlik, who has powerful bonds with the underworld, brings about a meeting between Aeron and a bunch of dead people from his past.

There are mermaids and other mythical creatures in the Ocean of Time.

Erlik practises a type of “Assassin shamanism”, where the basic principle is that he as an assassin serves the god of destruction (Erlik-khan), cleaning up the mistakes that the god of creation (Tengri-khan) has made. Even assassins have to make a living somehow, and killing people can be a lucrative business … But in order to figure out if a job is really in line with the path of the god of destruction, the assassins consult with the spirits.
Aeron is apparently a butur - a shaman in the “pupal stage”. According to Erlik, he has tremendous shaman powers lying dormant inside him.

Walking on water
One of the many tricks Erlik has up his sleeve. Knowing how to walk on water would be a really neat trick for any sailor …

Black magic
Samona is a master of these arts. Her sense of “black” is not that her powers would come literally from the devil and his demons (as opposed to God, Mary and Jesus in “white” magic). Instead, she draws power from “un-Christian” things like the forces inside living beings, objects, waters, forests, etc.
Most of the things she uses her magical skills for are rather ordinary, like mild good-weather, healing and accident-prevention spells, or a spell that keeps the fire in the galley from going out.

Willie discovers that she can hear Aeron’s thoughts sometimes. So far, he doesn’t know and she hasn’t told anyone about it, but actually she is not the only one. Samona can read many people’s thoughts, and Aeron’s are very clear to her. Aeron can also read Samona’s thoughts if she lets him. They’ve had some fun experimenting with it …
Some who have never experienced it (maybe because they are less susceptible to it [or because their minds have not been taken over by doggies, according to another theory]) might argue, but telepathy is actually not a supernatural thing!