Another hypothesis: possession is part of their talent. They wouldn’t be good entertainers without demons taking control over their bodies. Check what Beyonce said about her “alter-ego” Sasha Fierce (1:20-2:32):
I guess I wouldn’t be very entertaining on the stage, so Sasha comes out, she is fearless. She can do things that I cannot do when I’m in rehearsal.
Here is what Tony Glover said about Bob Dylan:
When he left Minneapolis he was just average. …. When he came back he was doing Woody, and he was doing Van Rock, and he was finger picking, he was playing cross harp. This is a matter of a couple of months.
So, “selling your soul” can roughly mean this: you serve the devil (help him to deceive people, take them away from the true God, make them blaspheme the true God) while he promotes you (with the help of “the elites” which are already serving him), he also helps you with the talent by possessing your body, he also tortures you in different forms (because he is simply full of hatred and envy). Proving your loyalty to the devil requires a ritual (breaking a commandment), which gives demons access to your body.
MK-Ultra often includes satanic ritual abuse: people are brainwashed and forced to participate in different satanic activities (including murdering other people), so it’s also very spiritual. It’s very very sad even to write this…
Here is the project called “50 Voices” where you can listen to MK-Ultra survivors. For example:
Possession is a common practice in acting too. Find some actors talking about it in this thread.