I was roleplaying two, but, they've vanished. I hope to hear from them again soon, but until then, here are some fresher ideas.
One is where a merman sees me in trouble in the water, and turns me into a mermaid to keep his race alive.
Another is where a mermaid, perhaps cursed, has to talk someone into wishing to be a mermaid, then they're free and the unfortunate human takes her place as a mermaid.
Another one is where Im surgically altered to be a mermaid for some reclusive billionaire.
If they appeal to anyone, please let me know.