Stonedeath is a goblin assassin, but much more than that. His new form allows him to scale walls, fight with uncanny agility, and above all that; he has a hatred for adventurers.
Renik Kavios is the leader of the dockworkers’ union. He is also a smuggler for stolen goods and illegal contraband. Through his power, he has the leaders of a city locked under his control.
If you want to add a "supernatural" touch to your campaign, define the rules of magic and the universe. Make your players comfortable with those rules. Then your new supernatural creatures must then break those rules.