I have a mermaid that became best friends with Caleb Vatore. I got his "turn" invite and went thinking "this isn't going to go well". Anyway when he finally popped the question I said yes. The popup came up 5 times and I said yes each time. Finally Caleb bit, fed, then fed her his blood and she got the strangely hungry mood let and the dark
energy smoke. I will let you know if she actually turns.
The other say I took one of my vampires and looked to see if turn into vampire option was available on a mermaid. It wasn't, so I assumed it wasn't possible.
At the time my above mentioned mermaid turning vampire was initiated she had started human but I fed her the mermaid kelp to make her a mermaid at the start of this particular game. And I was using MCCC at the time of the turning so it MAY be that.
But now it makes my want to see if it happens in a vanilla fame too...
Either way it was weird. I used to get vampire invites when I was playing an alien too but they never worked so I assumed this would be the same with mermaids.
This throws an interesting twist to my story however...