I watched it today and have some questions and maybe I'm not the only one.

1. The Empress is immortal, because she ate the mermaid flesh and is also immortal because of the snake. After the snake was removed from her body she should be still immortal, because of the mermaid flesh. So how can she die?

2. How can Bo Ya become a Shikigami? He is human. He sacrificed his blood yes and became the red fire bird, but I thought you need to die before you can become a Shikigami.

3. Bo Ya got hit many times with the snake tongue spikes, but he seemed to live. Didn't looked like that, after he got hit. He seemed to disappear.

4. How could he come back alive? Never thought a Shikigami can go back to his human body.

1. I'm pretty sure mermaid flesh is a simple translation error,  there were others.  She became immortal because she ate the snake.  

2.  Seems that being unconscious is enough to become one ? And that's probably why he didn't die at the end, because his physical body was alive. 

In the game there is also a woman that ate mermaid flesh so I don't think it is a translation error :/

I would have liked to see all four guardians incarnate