Abandoned God Arcs
Improve rare Abandoned Arc quality
Use Aficionado to improve the quality profile of Arc drops while farming skills.
Mission reward screen after a repeatable hunt that lists Abandoned God Arcs.
Repeat as long as you need better-quality Arc candidates. This is an ongoing random reward farm, not a one-time unlock.
Stop when you have suitable skills at the quality you need for your current build; switch to Arc Finder or a faster mission if the number of attempts matters more than quality.
Open a guide to find other locations and see what the item is used for.
Use Aficionado to improve the quality profile of Arc drops while farming skills.