note that this was part of a mega question split as requested
Fifth Question: Can Force Demons exist?
In the story, the father and his team create by accident a force demon, either by unwittingly tapping into the dark side of the force and thus creating a living representation of the dark side or simply created by a disturbance in the force. Is this possible or ever been tried?
I'm not an authority on SW universe further than original movies. However I think that assuming that the Force has it's source on a live being (knowns as "midiclorians"?) is reasonable to think that some type of entity could born from a dark side manipulation of the force.
Think in those "midiclorians" like cells. On real world live beings are large groups of specialiced cells that acts and thinks like a single entity.
It's only a theory (I don't know if there's some canonical example of that) but I supose that through dark manipulation of the force you can "group and bind" a sufficient quantity of those live beings to make them acquire some type of self-knowing and becoming thus a single entity.
However, I presume that something like that would be a very primitive entity (idk if "being" could be applicable to it), dark in it's source and probably formless. Could you call that "A Force Demon"? Probably that name would fit it very well, but I'd also bet that it's not what you first think in when hear that name.
Disclaimer: I'm not an authority on SW either (in fact, I'm not a real fan of most - but not all - SW stuff outside the original trilogy.) So, my answer is mostly speculation and extrapolation, from limited sources.
So, for the "Force Demon": We seem to have official creatures made of / living through purely the Force: Obi Wan's "ghost" appears and talks to Luke on several accounts (during the attack of the first Death Star, on Hoth etc), Luke has to face a manifestation of the Dark Side in the cave on Dagobah, Yoda has a conversation with Obi Wan's spirit on Dagobah, and in the end of RotJ, Luke sees the "ghosts" of Anakin (the returned Jedi) & Co.
Since not just one single person witnesses such ghosts, and the ghosts reveal new information unavailable to those whom they confer with (Yoda's existence and location, the looks of the young Anakin etc), we can assume that the ghosts are not simple hallucinations but conscious, independent entities - and they live solely in and through the Force. So, Force entities already seem to exist in the canon - and there's no reason why you couldn't call such an entity of the Dark Side (such as the apparition that attacked Luke in the cave) a "demon", though I'd personally pick a different name, as "demon" is too... "Earthly". :)
As for the artificial creation or "summoning" of such a creature: Luke did just that when he wandered into the cave armed, despite Yoda's warning.
Edit: AFAIK the C-Canon Knights of the Old Republic computer game even featured a Sith spirit, that is, a Dark Side "ghost", an ancient Sith master called Ajunta Pall.
In Jedi vs. Sith: The Essential Guide to the Force, there are many entries of Sith becoming "ghostly incarnations" which could be considered demons:
There is a long history of Sith Lords and dark siders who abandoned their physical forms upon death to become one with the Force, and return to the material realm as ghostly incarnations. (Page 176)
Examples:
"the spirit of Dark Lord of the Sith Marka Ragnos had survived in the toms of Korriban" (Page 201)
"...Freedon Nadd, a former Jedi apprentice who learned the ways of the Sith from the spirit of Naga Sadow." (Page 175)
"More than three hundred years after Nadd's death, his spirit trainined another renegade Jedi, Exar Kun..." (Page 175)
"Exar Kun's spirit was trapped for four millennia in the temples of Yavin 4" (Page 175)
In the SW universe legends and canon the force ghosts are neither light nor dark they are just the force and mainly grey Jedi can become them because they represent a balance in between the light and the dark. There are two sides of the force, the cosmic force and the living force. When someone is alive their a part of the living force and when they die they become a part of the cosmic force but when someone has training or is qualified they become a force ghost that is visible to all the spirits of the dark side are actually just sith magic/ sorcerery and dark side force techniques meant to keep the dark side immortal or alive forever.
