I can kind of answer your questions. (1) the priest has a past because before he meets the MC he was alived but died when he entered the cave (based of my understanding of the story) then was able to come back alive because of the pearl, he was dead for a short time so he wasn't able to realize that he died. (2) i think they were able to go back to the human world because of the MC blood because the demon gods piwer i what keeps them alive. (3) yes the thing about being pregnant was a joke... However, despite me explaining thi when you probably forgot about it haha,, i do agree that the ending was rushed, it felt like there is more of a filler chapters than the actual plot..
So many plot holes,
Didn’t priest slave ML need the pearl our MC has to be a person so why does he have a whole past? What was the point of that pearl? Also the fact there’s basically no explanation as to why he’s back in the human “world” with all the mermen at the end. Nor do we really go into detail about his life in his “world”. Also what was that about priest shadow ML being pregnant? Was it a joke? If it was they seemed serious. The ending just seemed a tad rushed. I mean I get it, they dragged the story for a long time but didn’t really answer a lot of questions and only made more so they just wanted to bring it to an end. But seriously like what about the chief wives? Was the mark made by the stalker merman not permanent? It looked really painful though.