So after finishing all the new enemies myself I thought I talk shortly about how I did it and what I learned from it.
Pretty much doing itself if you go for kongamatu and regulary run the content
Trickiest of the three as it includes farming every of them in the night instance and reseting to day and repeat.
Helped that at one point I made a map of them and their flightpaths. Kill each of those, repeat and you should make the best possible progress:
Take the mission “wraith of the dawn” kill all of them on the rocket launcher step and reset the instance by going to the character select and getting back in again. There are roughly 60 of them up there and a few spawn in the foundling area every time (if you think the running around is worth it). Should give you the 2k pretty fast.
Not much to say about else…if someone finds a better way I am happy to hear it. I have a habit of picking suboptimal farming methodes.