Heartwarming / This Book Is Full of Spiders: Seriously, Dude, Don't Touch It
The reunion of John and Dave, where John thinks Dave is a monster (a different, more terrible monster) but still goes to him.
The long-awaited reunion of Amy and Dave, complete with bone-crushing hug and happy tears.
The reveal of Anna's true form, her apology to Dave, and him hugging her (albeit confusedly).
The moment when Molly sacrifices herself for Dave, just in time to prevent Dave from dying for Amy.
Anna, in a twisted sort of way.
As usual, just about everything Molly does.
Amy. The second she gets it into her head that David needs her she's on a bus racing towards Undisclosed with some of the world's best cupcakes.
It's a somewhat twisted case, but when John thinks that David is dead he holds it together for a little while and then pretty much falls apart. Amy thinks he's just being an alcoholic bastard, when in reality the man is devastated that his friend is dead. Really shows how much David means to John.
This is reinforced much later when time is frozen and David is about to take the bullet for Amy. John suggests that the pair of them screw off to enjoy the paused world, just him and David for as long as it lasts.