Before I Change My Mind

The hero has the villain captured, in his grasp, and there's no way the villain can escape the due justice that's coming to him. As soon as the police show up, the hero informs his foe, the villain's going off to jail and will get his just reward.

However, the villain responds by trying to convince the hero that he (the hero) has to let him (the villain) go free. The reasons he'll give may vary, but most usually they'll involve the point that without the villain around to enforce his particular brand of evil, someone more brutal than he is will inevitably show up to fill the void and potentially make the status quo a whole lot worse than it is at current. Or, the villain might have a very good reason for doing what he's been doing, and will let the hero know as much. Or, if the villain goes to jail, the hero won't have much other purpose in life.

Cue the hero freeing the villain from his bonds and telling him to leave now "...before I change my mind."

Alternately, reverse the scenario: the villain has the hero in his grasp and is ready, willing and able to kill him, but the hero says or does something that somehow convinces the villain not to go through with it. Or maybe the villain can't go through with it because Even Evil Has Standards, the hero has to live to serve a specific purpose, or the villain's existence will be utterly empty without the hero being there to oppose him.

As a result, the villain decides to free the hero and tells him to get lost "...before I change my mind."

What is being showcased here is an example of someone (however briefly) looking the other way or granting permission in some other manner, allowing someone else to do something they want to do, escape a particular situation, or otherwise fulfill a stated objective.

Aside from the examples listed above, the words may be used if the hero and villain had come to some kind of deal (whether on-screen or behind-the-scenes), and the villain says them to indicate that he just managed to not go back on his word.

It also doesn't necessarily have to be between a hero and his villain; a Big Bad, for example, may allow an underling to pursue a course of action, but if the underling hesitates in leaving, the boss may advise him/her to get to it, citing the trope's name in the process.

Note that the exact words of the trope name don't necessarily have to be quoted in order to qualify. Alternate phrases may include "while I'm still in a good mood" or "while I'm still feeling charitable."

See also Can't Kill You - Still Need You and I Gave My Word, which are situations where this may be invoked. This might also happen because the hero/villain is a Slave to PR. An Enemy Mine situation may sometimes result in this, as well.

Film - Animated
"Lord Farquaad: (to Shrek) Very well, ogre, the deed to your swamp, cleared out as agreed. Take it and go, before I change my mind."
 * Shrek gives an example of the "deal-between-hero-and-villain" variant:

"Edna: You need a new suit, that much is certain. Bob: A new suit? Well, where the heck am I gonna get a new suit? Edna: You can't! It's impossible! I'm far too busy, so ask me now before I can become sane. Bob: Wait? you want to make me a suit? Edna: You push too hard, darling! But I accept!"
 * The Incredibles plays this one a little differently:

Comic Books
"Wolverine: Get yer act in the wind, bub...'fore I change my mind!"
 * In one issue of X-Men, Wolverine and Rogue are in the Savage Land and have joined up with foes Brainchild and Gaza to transform Sauron from his pterodactyl form back to humanity. Sauron calls them out for trying to force the change on him, seeing as he's quite comfortable being Sauron instead of his former human self, and then points out that if he's not around to maintain his rule over the Savage Land, someone else will come along and take over anyway. Wolverine pauses a moment, then unsheathes his claws and severs Sauron's bonds before advising him to flee.

Film - Live Action
""Lead me to your cross and break me, bleed me, beat me, kill me, take me now--Before I change my mind!""
 * An odd twist in Jesus Christ Superstar. At Gethsemene, Jesus asks God to spare him—then finally, angrily, gives in:

"Eric: [to Mr. Luce] Get out of here, before I change my mind. Go!"
 * Elephant: Eric has brought a gun onto campus so he can get kill some people as revenge for being mistreated. While he's confronting and bullying an adult (Mr. Luce), he turns and shoots a student.

"Iqbal Riza: Oh there's no way you're going to win this thing. Omer: I know, I fear as much. Iqbal Riza: [Sighs and looks him up and down, then takes Omer to his stage] Get up there, up on the stage. Omer: Are you sure? Iqbal Riza: Do it! Before I change my mind. [He then gives Omer advice on improving his performance]"
 * American Dreamz: Iqbal had hoped to get on the title talent show, but Omer was chosen instead. Iqbal becomes Omer's manager, but he's bitter about not being on the show. Iqbal is now watching Omer rehearse.

"Castlebeck: Here I am smack-dab in the middle of a moral dilemma, Randall. You've torn this town to shreds with that little escapade of yours, you and your Eleanor. But I understand what brought you back here. A brother's love is a brother's love. You saved my life, didn't you? So, what am I gonna do? Memphis: It's your call, Detective. Castlebeck: Get out of here, Randall. I'll clean this up. Go, Randall, before I change my mind. Go."
 * Gone in Sixty Seconds. Randall "Memphis" Raines has killed Calitri as he's about to shoot Detective Castlebeck.

Live Action TV
"John Casey: We, meaning I, will find Lizzie. You get Chuck. Well go, before I change my mind."
 * Chuck episode "Chuck Versus the Marlin". John Casey and Sarah have just been ordered to get Lizzie. Casey is known for strictly following orders.

"Sheriff: Something tells me you folks are tellin' the truth. Boss Hogg: [Makes a sarcastic comment] Sheriff: [interrupting] Get him outta here before I change my mind!"
 * The Dukes of Hazzard episode "The Dukes in Hollywood". The Dukes are trying to convince the sheriff to let them go so they can catch a swindler.

"Commander Adama: Reinstate the trainees to flight status. Do your job. And walk out of this cabin while you still can."
 * Battlestar Galactica: Commander Adama, after he finds out that  was responsible for his younger son's death.

Theater
"Jean Valjean: This man's done no wrong, and he needs a doctor's care! Javert: I warned you I would not give in. I won't be swayed! [snip] Jean Valjean: Come, time is running short. Look down, Javert, he's standing in his grave! Give way, Javert! There is a life to save! Javert: Take him, Valjean, before I change my mind! I will be waiting."
 * Les Misérables:

Western Animation
"Chief Wiggum: On your marks, get set; now get outta here before I change my mind. (bang)"
 * Parodied on The Simpsons by Chief Wiggum in one episode, when he's starting the Springfield Marathon.

"Homer: Oh. Better hurry up."
 * A straighter example occurs when Homer charges $1000 to the company insurance for a hair restoration product. Mr. Burns doesn't fire him because he recalls his own hair loss and then tells Homer to get out of his office before he reconsiders.