Drink every time an antagonist becomes an ally.
The movie that made me fall in love with this trope is The Fugitive. We’re rooting for Dr. Kimble (Harrison Ford) from the beginning since we know he’s innocent, so Deputy Gerard (Tommy Lee Jones) seems like the obvious villain as soon as he gives his famous speech about searching for Dr. Kimble in every “warehouse, farmhouse, henhouse, outhouse, and doghouse.” But gradually we find ourselves rooting for Deputy Gerard as well, almost against our will. He’s a good man who’s doing a good job of trying to catch Dr. Kimble, and even though we don’t want that to happen, we admire his integrity and savvy. What makes this trope so satisfying is the moment you realize you’re actually supposed to feel this way, that the film has been leading you this direction all along without making it obvious that Gerard is actually a good guy. For me this happens when Gerard and his team start to put the pieces together about the one-armed man–we know him so well by this point that we trust him to do the right thing with this information and bring the right man to justice.
Easily one of the most affecting iterations of this trope is Terminator 2: Judgment Day, where the villain of the original Terminator (Arnold Schwarzenegger) returns for the sequel, but as a good guy. Incredibly, the film doesn’t reveal the T-800’s motives until he and the T-1000 (Robert Patrick) have John cornered in the hallway. The T-800 pulls a shotgun out of a box of roses and we genuinely don’t know who that bullet is intended for until he pushes John out of the way. Of course, the trailer spoiled this for the bajllions of people who went to the movies in 1991, but how cool would it have been to go into this film thinking of Schwarzenegger as the bad guy until that moment? We also get to experience this rapid change of heart through Sarah Connor (Linda Hamilton), who acts out the visceral fear we feel when we first see the T-800 again, and then has to recalibrate her expectations of him when she encounters a new, more terrible enemy than the one she faced before. It’s not unlike Ripley’s reaction in Aliens to finding out Bishop is a synthetic, after being betrayed by an earlier model in Alien. Both heroes have been traumatized by their experiences and can’t simply switch off the fear and revulsion they feel just because these newer cyborgs assure them that they have been programmed to help and can’t possibly endanger them.
Of course, sometimes the hero has to actively enlist the help of a lesser villain in order to fight a greater one, the way Clarice (Jodie Foster) calls on Hannibal Lecter (Anthony Hopkins) for help in tracking down Buffalo Bill in The Silence of the Lambs. In this case she has no assurance that she’s safe with Lecter, just the knowledge that he’s the only one who can help her. Lecter gives her a set of ground rules to abide by in order to purchase her safety—she has to answer his questions, fully and truthfully. Even then, we get the feeling Lecter is toying with her, that he could kill her as easily as putting on his socks if he chose to. She lives because he finds her amusing, because she breaks up the monotony of his days. And yet there’s an uneasy sense of camaraderie about their relationship: teaming up to find Bill has brought them together in a way Clarice doesn’t want, but it ends up helping them in other ways—after all, Clarice has lots of demons she hasn’t confronted, and Lecter is still a psychiatrist in search of a patient.
Finally, I couldn’t talk about this beloved trope without mentioning the T-Rex in Jurassic Park. Much like Hannibal Lecter, the T-Rex is only dangerous if you don’t play by its rules—or, in the case of the two kids entrusted to Dr. Grant (Sam Neill), if you don’t know them. The real villains of the film (at least the animal villains) are the velociraptors. They’re agents of chaos who kill for sport, and we are genuinely relieved when the T-Rex eats them at the end and saves the day. It’s oddly satisfying to see a dinosaur that’s every bit as terrifying as the xenomorphs in Alien come to our protagonists’ aid, even if he’s helping unwittingly. It shifts our perspective, which is what all great movies do in one way or another—the character we’re watching is the same, but it’s us that has changed.