Dredge

Rarely seen at the surface, Dredge was once a pirate (or so he claims). Fascinated by the underwater world, he made a deal with a vampire to grant him the power to turn into  fish in return for a monthly tithe of sunken treasure.

Some might take being allowed to turn into a hagfish as a curse, but Dredge loves it. He's a little loopy from spending so much time down there with just other marine creatures. He can barely remember his human life, and only comes to land once a month to hand in his required tithe.