Grumpy old man reluctantly raises a child that he accidentally adopted. (Heidi, Silas Marner).
Underdog loses but still wins in sports movies.
Nobody listens to the scientist warning of “coming calamity”.
Two strangers are forced to pretend they’re married.
Old/eccentric person explains arcane lore to the heroes.
The "hero/heroine" turns out to be the villain.
Random but endearing side character meddles in main characters’ lives.
Character you thought was too old/drunk/frail to be of any help pulls it out of the bag when needed.
Hero and villain have a temporary truce for a common goal before going back to fighting each other. (Prof X and Magneto, Dr Who and The Master)
Parent (usually father) who disapproves of their child’s choices (usually sport) sees them smash it at the finale and proclaims “that’s my son/daughter”. (Circus Boy with Mickey Dolenz. Sometimes father says "I shouldn't have ridden you so hard", and son says "I love you, Dad!")
Protagonist gets beat up and torn to shreds, but they keep going with their last bit of strength.
The brilliant aberrant who has no social ability but sees what no one else sees. (Holmes, Saga Noren)
All the friends they've met along the way show up together for the final effort. (Including the friend they’ve fallen out with.)
A character remembers something someone tried to tell them earlier that is exactly what they need to save the day in Act Three.
Villain/Morally Gray Character is hired to infiltrate the hero's friend group to betray them but then they start to actually care about the heroes and switch sides to protect them. (Bosola)
Two rivals are thrust into a climactic battle. They fight to a draw, gain respect for each other in the process (and maybe even realise they are just pawns in a larger conflict.) They join forces to fight the REAL enemy.
Irritating jokey guy suddenly gets serious. May say: “Nobody took me seriously so I played the fool deliberately.”
Hero covertly escapes his restraints during a villain’s monologue. ("Why are you telling me all this?)
Nice, meek guy is forced to navigate the criminal underworld - and proves to be surprisingly good at it. (He is probably an insurance investigator.)
Story starts with protagonist waking up with amnesia and/or in an unknown place with no clue how they got there. (Traitor's Purse, Margery Allingham)
Great big fiery explosion dies down a bit, and then one solitary burning wheel rolls slowly out of the wreckage.
A struggling musician type has a friend who keeps trying to get them to “sell out” and work with them at their evil corporate ad agency writing jingles for commercials. (Keep the Aspidistra Flying, George Orwell)
"Your family never told you what really happened in that story that you thought you knew."
“For 23 years, I've been dying to tell you what I thought of you... well, being a Christian woman, I can’t say it!” (Wizard of Oz)
(Thank you, Twitter.)
More here, and links to the rest.