Use a decent shotgun w around 600 ammo and a cactus broth tgen you can do the boss solo

Take a few good pumps and cactussoups and shoot at his arms! Dont get to near to the nameless and Reapers!

Well i recomdmend getting artifacts for it on other maps and then transfer it to aber it will be much easyer like that also u can start bossfight with any of drops there so u have not to go to terminal and yea dont forget ur cactus broth

The artifact in the radiation zone is not that hard to get, there is a reason ark supplied us with a rock drake, and the reaper king send that sucker off to kill whatever he pleases while you go get your artifact