Back to the Future Part II

Back to the Future Part II is a 1989 American science fiction movie directed by Robert Zemeckis and written by Bob Gale. It is the second movie for the "Back to the Future trilogy". It stars Michael J. Fox, Christopher Lloyd, Thomas F. Wilson and Lea Thompson.
Plot.
Dr. Emmett "Doc" Brown (Christopher Lloyd) appears in 1985 in his time-traveling DeLorean and tells Marty McFly (Michael J. Fox) and his girlfriend Jennifer Parker (Elisabeth Shue) that something is wrong with their future children, and that Marty and Jennifer must come with him to the future to fix it. As the three of them leave in the time machine, they are accidentally witnessed by Biff Tannen (Thomas F. Wilson).
Doc takes the DeLorean to 2015, thirty years in the future. Jennifer keeps asking questions about her and Marty's future marriage, causing Doc to use a sleep-inducing generator to knock her out, explaining that no one should know too much of their own future. Doc reveals to Marty that his future identical son, Marty Jr. (Michael J. Fox), was imprisoned after a failed bank robbery in which he was forced to participate by Biff's future grandson Griff Tannen (Thomas F. Wilson). Marty's future daughter Marlene (Michael J. Fox) attempted to break Marty Jr. out, only to be caught and imprisoned herself. Doc explains his plan: to have Marty pose as his future son, refuse to participate in the bank robbery with Griff, and return to 1985 so his future family can live a happy life. Doc gives Marty futuristic clothes so he can look the part, and they leave an unconscious Jennifer in an alley. 
Marty explores a futuristic Hill Valley and enters the nostalgia-themed Cafe '80s, where he's supposed to meet Griff. Marty meets an elderly Biff and almost runs into Marty Jr., who Griff bullies when he arrives at the cafe. Marty swaps places with his son and confronts Griff, refusing to participate in the robbery. Griff calls Marty "chicken", which triggers Marty and causes a fight between him and Griff's gang. Marty steals a hoverboard and uses it to escape. Griff and his gang try to hurt Marty on their own hoverboards but are knocked off balance, crashing into the courthouse mall at the city center. Griff's gang is arrested and the future changes, with Marty Jr. no longer going to jail. Marty keeps the hoverboard and buys a 2015 sports almanac to take back to 1985, in order to unfairly bet on sports results. Doc finds out and scolds Marty. They try to get back to 1985 but find out that Jennifer has been found by cops and taken to her future home. Doc throws away the almanac, but the elder Biff retrieves it from the trash and steals the DeLorean. Jennifer wakes up in her future home, where she sees older versions of herself and Marty and her future children. She watches as Marty's future self enters a shady business deal and is fired from his job. Doc and Marty intervene in time and bring Jennifer back to the DeLorean, and return to 1985.
Marty quickly figures out that the timeline has been changed, with Biff now a rich tycoon who made his fortune by betting on sports results since the 1950s. After learning that his mother Lorraine (Lea Thompson) is married to Biff against her will and his father George (Jeffrey Weissman) is dead, Marty works with Doc to figure out what happened; they realize that the elder Biff from 2015 stole the DeLorean in order to give the almanac to his younger self