I have tried this challenge a couple of times now with no success. The description of the challenge says you need to “Have a warpfire thrower kill 10 enemies for you.” , but after getting him to kill well over 20 enemies the challenge still wasn’t completed.
I later tried not attacking and not pushing the enemies in any way, but after killing more then 10 of them the challenge still didn’t register.
No one else seems to have this problem as far as I know (only 2 of my friends who I play with), because I haven’t seen any online posts about it.
I mostly tried this in weaves btw, but also in base game.
If you have any tips I’m open to suggestions, but I believe the challenge is simply bugged.