On bloody harvest : descent into heck after you talk to Maurice check your side mission menus there’s a side quest to Search the galaxy for a ghost ! where to search the ghost ? well they spawn in groups of normal enemies, just find the one with green aura !
electra city voracious canopy and slaughters
Search The Galaxy For A Ghost Borderlands 3
You can go to Jakobs Estate at Eden-6 in the varacious canopy
Or just started a run through all the boss / mini boss/ rare spawns and by Drought there was ghostly versions appearing with random spawns
Remember the one that you need to kill is the one who have a green aura surrounding their body
after you kill them, a big green head skull will spawn and flying towards you.
Shoot it and you’re done ! also notice that there will be a new quest : Search the galaxy for Hectoplasm 25. You can get hecktoplasm from the green skull ghost 🙂