Can't post in Elite, sorry if this is a repost due to this condition.
This one involves the groups of mechs infront of the final boss (Engine Guardian) door. Typically only the last mech killed drops loot, but by pulling and dying to the mobs--in order to reset them--they all drop grand soul gems (~60 per pull), white items (typically ornate/intricate), and each has a chance to drop blue/epic rings which are typically the reward for completing the entire encounter. Making about 3k/pull and each pull takes no more than four or five minutes.