Curse Catcher

What I did was took the name, and creature type for a Magic the Gathering Card

it was called Curse Catcher and it was a Merfolk

The direction of the original was a wizard, using magic or curses

I wanted to go the Werewolf direction of Curse, so he started out as a regular Merman, but slowly gets changed more monstrous.
and made him Cursed, and I also wanted to make him a warrior in a sort of way, and so I went with a Shaman.

Shamans use pieces of animals and such to get into the spirit world, and can enter people's souls that way, and often times it's for healing. I imagine that's how his curse gets worse, he goes into peoples souls and removes what's not supposed to be there, but that becomes part of him transforming him further.