So there is an allegedly real phenomenon called "loosh farming," wherein disembodied astral spirits harvest some kind of emotional energy from the emotions of humans on earth.
Robert Monroe wrote about this in the book Far Journeys. I don't claim that this is real in the real world, but I do claim this would be awesome in the Old World of Darkness.
As I recall, changelings can harvest emotional energy from human emotions. However, changelings are embodied people, not disembodied spirits. Mages might be able to do something with Mind and Prime spheres, but mages are also embodied people.
So to get the "disembodied astral spirit" thing going, I think the "loosh farming" must be done by Umbrood.
However, I don't know how to do this with Old World of Darkness rules. I don't even know whether it's possible.
Example emotion-control effects include "Haunted Heart" (Changeling Chicanery 4) or Mage Mind Sphere 2.
I had hoped to cite Umbrood charms, but I can't find any that seem relevant.
Actually, Wraith the Oblivion might be a very good fit for this. (Page 137 of Wraith explains that Wraiths with Keening can induce emotions, and then try to feed off those emotions with a difficult target of 9. )
Originally, I was thinking that Werewolf rules for Umbrood might have Charms suitable for getting Gnosis points out of human emotions, but I have looked at all the Charms I could find and nothing seems to fit.
As it is, the only way to do "loosh farming" would seem to be a two-part venture involving an emotion controller (e.g. a Mage with Mind Sphere) and several compatible Wraiths. The emotion-controller would induce appropriate emotions in normal humans and the Wraiths would keep trying until they could raise their Pathos from the induced emotions.
If there are Umbrood rules comparable to the rules from Wraith or Changeling, I would like to know the title of the book that contains those Umbrood rules.