I'm not sure what Preacher has to do with anything, but here's what happens:
Vexing Devil resolves and enters the battlefield.
Two triggers occur, but the order doesn't really matter. One is for Pandemonium to deal 4 damage to whatever target the Devil's controller chooses, and the other is for you to choose if you want to take 4 damage and force the Devil to be sacrificed. These don't particularly affect each other, even if the Devil's ability resolves first and you force it to be sacrificed, the 4 damage from Pandemonium will still resolve.
You can activate Preacher in response to these triggers or after they resolve, but even if you gain control of the Devil, you don't get to change the target of the Pandemonium trigger, and the Devil's ability is still asking you to take 4 or force the sacrifice. In this case, I assume you would want to not take 4 damage from the Devil so you can keep the Devil, but you might still take 4 from Pandemonium, or if the target of Pandemonium was the Preacher, that would still resolve and the opponent gets the Devil back.
I'm not so sure about the Pandemonium trigger. No question about the target selection, which is done when the trigger is put on the stack. However, it says "its controller may ...". And that choice is made upon resolution. With a change of control in response to the trigger, I think, the new controller has to make that choice, making it possible to essentially negate the trigger by choosing not to have the creature deal damage.
Jim has has the choice to take 4 damage - interestingly, he keeps the Devil whether or not he takes the damage - The other player controls the trigger, and can't sacrifice a creature he doesn't control.
Pandemonium trigger moves to resolve. Jim, as controller of Devils, has the choice of whether or not to deal damage to the target his opponent selected (probably not, just guessing).
1. I have Preacher out for awhile
2. Opponent plays Pandemonium
3. Opponent then plays Vexing Devil
4. I play Preacher, and he only has 1 creature
Not too sure about the order of what will happen. Anything helps!
Vexing Devil resolves and enters the battlefield.
Two triggers occur, but the order doesn't really matter. One is for Pandemonium to deal 4 damage to whatever target the Devil's controller chooses, and the other is for you to choose if you want to take 4 damage and force the Devil to be sacrificed. These don't particularly affect each other, even if the Devil's ability resolves first and you force it to be sacrificed, the 4 damage from Pandemonium will still resolve.
You can activate Preacher in response to these triggers or after they resolve, but even if you gain control of the Devil, you don't get to change the target of the Pandemonium trigger, and the Devil's ability is still asking you to take 4 or force the sacrifice. In this case, I assume you would want to not take 4 damage from the Devil so you can keep the Devil, but you might still take 4 from Pandemonium, or if the target of Pandemonium was the Preacher, that would still resolve and the opponent gets the Devil back.
Does that answer the question?
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