And I mean like ghost possession or demon possession. What do you guys think about possession in Star Wars? Like, does it exist, do they fit in the lore/saga? Has any character been possessed by a Force ghost or some sort of demon?
There's been quite a few instances of it in canon. Ahsoka was possessed by the Son in the Clone Wars episode Altar of Mortis. Dooku was briefly possessed by Mother Talzin to fight against Darth Sidious in the Darth Maul Son of Dathomir comic. The recent Darth Vader comic series had the mask of the ancient Sith Lord Momin possessing Imperials on Mustafar. In the Rebels episode Visions and Voices Kanan and Sabine were possessed by Nightsister spirits. I guess you could also count the Clones infected by the Brain Worms in TCW as demonic in a way too.
It seemed to me that Sidious was possessed in Revenge of the Sith when he gave Anakin the Vader title.