If a fourth subspecie of Mermaid from Celtic folklore existed in the universe of Demonic Paradise, what would it be?
The question is a bit silly, but I like the idea of a Celtic subspecie of Mermaid. Celtic culture has always had many influences on the Mermaid due to the innumerable versions of the latter.
Since in the Demonic Paradise universe the Merrow, Selkie and Morgen are already on the bench. I think it could be the Ceasgs or the Finfolks. The Ceasgs are interesting, but they lack legends and make them less known in terms of lore. As for the Finfolks, the latter are interesting but personally I see them more related to the Merfolks than to the Mermaids.
This is just a suggestion, not cast gold, however I like this Wiki.