In the Yellow Submarine movie plot, the Blue Meanies are the ones who are forced to retreat. The Blue Meanies are music-hating creatures who launch a surprise attack on the music-loving paradise of Pepperland. Old Fred, Ringo, John, George, and Paul travel in the Yellow Submarine to return to Pepperland and, upon their arrival, they work together to save Sgt. Pepper's Lonely Hearts Club Band and eventually defeat the Blue Meanies, forcing them to retreat.<|im_end|>

 Based on the plot you provided, the answer to your question "Who are forced to retreat?" is:

The Blue Meanies are forced to retreat.

According to the plot, the Blue Meanies launch a surprise attack on Pepperland, but the Yellow Submarine and its passengers, led by Ringo, successfully make their way back to Pepperland and defeat the Blue Meanies, restoring color and music to the land. The Blue Meanies are not mentioned as retreating or being defeated, so it can be inferred that they are the ones who are forced to retreat.<|im_end|>

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Answer the following question: I am a movie director and I just received the following movie plot. Could you help me answer this question? If not, let me know by writing "Not answerable".  Plot title: Yellow Submarine Movie plot: Pepperland is a cheerful, music-loving paradise under the sea, protected by Sgt. Pepper's Lonely Hearts Club Band. The titular Yellow Submarine rests on an Aztec-like pyramid on a hill. At the edge of the land is a range of high blue mountains. The land falls under a surprise attack from the music-hating Blue Meanies, who live in or beyond the blue mountains. The attack starts with magical projectiles fired from big artillery stationed in the blue mountains. The Blue Meanies seal the band inside a music-proof blue glass globe, they render the Pepperlanders immobile as statues by shooting arrows and dropping giant green apples upon them (a reference to the Apple Records music label), and drain the countryside of colour. In the last minute before his capture, Pepperland's elderly Lord Mayor sends Old Fred, an aging sailor (whom the mayor calls "Young Fred"), to get help; he runs to the Yellow Submarine and takes off in it ("Yellow Submarine"). Old Fred travels to Liverpool ("Eleanor Rigby"), where he follows the depressed and aimless Ringo and persuades him to return to Pepperland with him. Ringo collects his "mates" John, George, and finally Paul in The Pier, a house-like building on the top of a hill. The five journey back to Pepperland in the yellow submarine. As they start learning to operate the submarine, they sing "All Together Now", after which they pass through several regions on their way to Pepperland:  Sea of Time â where time flows both forwards and backwards to the tune of "When I'm Sixty-Four". At one point, the submarine passes itself as it loops through time. Sea of Science â where they sing "Only a Northern Song". Just before the song finishes, they pick up a monster. Sea of Monsters â The monster is ejected into a sea inhabited by other weird monsters. Ringo presses the panic button on the submarine, ejecting him from the submarine and into the sea. He is seen riding one of the monsters, who tosses him around, and with the threat of Native American-like creatures, resulting in John... My question: Who are forced to retreat?
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