A well-loved character from a previous installment returns, but not in a happy context

Peni Parker (Across the Spider-verse): one of the most popular characters in the first movie returns after many concerns that she, Noir & Ham won't be in it. Only for her to show up looking absolutely miserable, a complete 180 from her happy-go-lucky personality from the first movie, in her few seconds of screen-time and the entire mood of the scene (Miguel explaining Canon Events & Miles learning that his dad is going to die during the Spot's rampage) changes everything for the worse, even more so if you read the comics she's from, her being inspired by Evangelion & the fact she willingly subscribes to Miguel's Canon Event Theory (until the end of the movie, that is)

Shrek & Donkey (Puss in Boots: the Last Wish): the most popular duo from DreamWorks' most popular franchise briefly return to the big screen for the first time in 12 years, and it's in a flashback of Puss's lives when he first fights the Big Bad Wolf. As a wise giant enemy crab once said, we're not supposed to cheer over the fact that we're seeing them again, we're fearing over the fact that Puss might never see them again.