@mistystarshine apparently wrote a Hazbin hotel mermaid AU called The Drowning Time and there's a line that caught my attention. "If a human who’s done enough terrible things dies at sea, there’s a chance that they’ll come back to life as a siren..."

...so obviously I had to put way too much thought into what an Alastor mermaid would look like lol. Somehow settled on a Louisiana/American alligator as his mermaid base but, er.... but maybe that would make him a centaur instead?? IDFK lol. Added some fishy-fins to his limbs and ears to balance it out a bit.