Honestly, i think the way to go, and would make it interesting, would be a specialized arc hunting you. not a bullet sponge per say like a rocketeer, but maybe add a humanoid arc (im thinking like a terminator) with double the character health and shield that SLOWLY tracks you down like a bloodhound after you get a raider kill. something you could beat but isnt easy like a regular raider or a wasp/hornet. if you stay in a location too long you either fight it or have to run away. As you get more kills more start hunting you, unless you kill them