Grinding for this is frustrating enough to take the fun out of getting the Blackstar set and sometimes even playing at all.

There seems to be little info on drop rates and where best to try.

With the new Sub-Weapon being added this can only get worse, as many drop areas are highly contested and most likely will result in getting PKD and pushed out

I would like to see this become a market place item like so many other drops, and maybe we could have an event boost when they add the Sub weapon 

This item long lost it's purpose. It's drops like trashloot, and only an issue for new/casual players, not like it would even worth it the effort to craft it yourself.

You don't need specters energy for weapons

And bs armors is just a trash armors, PA make this armors to solve the problem of caphras out of stock in KR but they failed because it didn't solve anything so they abandoned this project and increased the caphras loot rate (wish they should have done from the start instead of wasting their time with bs armor)

Bs armors is like khan heart, useless because abandonned project

You need it for awa weapon, and mostlikely you will also going to need it fo sub weapon...

But yeah, it's a kinda failed project.

I'm full pen Black star and yeah if you plan on going past C10 or fighting human mobs than yes it's a failed project. Blackstar anything is good if you don't want to sit thumbing at your nose waiting on Caphras  on the marketplace and because you can get the flame and then turn in for Fallen God and furture Labreska's helmet without going through that trouble (it's superior in that regard to regular boss armor). As far as fail stacking goes it will be rough getting pen blackstar below 200 FS unless you are extremely RNG carried. Main hand weapon you just need the remnant but for every other piece you will need a remnant and spectres which has a high chance of dropping apparently in Valencia areas (I got five extra in my storage). Hope this helps and good luck to you.

That thing is nightmare to get, but if you are lucky you can get it just like that, but most likely you are about to grind to insanity, getting Specter's Energy is more like a job than a game that is against any basics of game design.