For the cursed thralls, I was hanging out in the Cosmodrome, in one of the transition areas, where you first meet the Hive in the story, the Servant of the Hand stays in the corner from the DLC. Clear out the area, shoot the Servant, and then go near the exit just near the stairs that lead to where you fight your first wizard. From that position, enemies that are spawNed by the Servant won't follow you, so just take your time and shoot the normal thralls that you see and the knight that spawns. Once they'really ckeared, just get close enough to cause the cursed thralls to start coming y o you. Then just kill them one at a time, after you kill one, go back on the stairs and heal. Rinse and repeat. That was also where I did the fusing rifle/thrall bit.