Supergirl does not spare Krem of the Yellow Hills at the end of the film. Instead, after Ruthye Marye Knoll has spent the story chasing him across the galaxy, Supergirl takes Ruthye's sword and kills him with a fatal stab.
That is why people are looking for a Supergirl post-credit scene now: the ending lands as the movie's biggest shift from Supergirl: Woman of Tomorrow, and it changes the moral center of the story in one hard stroke. Ruthye finally finds the man who murdered her family and poisoned the hero's dog, but the revenge that drove the film is not handed back to her. It is carried out by Supergirl, who spends most of the journey rejecting Ruthye's plan to kill Krem in anger.
The comic miniseries moves in a different direction. In Supergirl: Woman of Tomorrow, Ruthye cannot land the final blow no matter how many times she tries, and Supergirl decides to kill Krem herself only to spare Ruthye the price of vengeance. Ruthye then stops her, Supergirl sends Krem to the Phantom Zone, and the story later jumps to an elderly Ruthye and an eternally young Supergirl. Even there, Krem is not simply forgotten; after enough lifetimes in self-reflection, he repents, and the older Ruthye ultimately strikes him with her staff instead of forgiving him.
The film keeps the same chase but changes the ending that gives the chase its meaning. Craig Gillespie and Ana Nogueira have clearly chosen to make the movie work on different terms, and the result is a version of Supergirl that is willing to cross the line she has argued against for the entire film. It also makes Krem feel different from the comic-book version; Matthias Schoenaerts plays him less like the closer analogue to Tom Chaney from True Grit and more as the man whose punishment arrives immediately rather than after reflection.
That choice leaves the cleanest question behind the search for a post-credit scene: not what happens after the stabbing, but what this ending says about Supergirl and Superman in this DC Universe. The film's last move rejects the usual superhero restraint associated with characters who wear an S on their chest, and it does so at the exact moment Ruthye gets the revenge she has been chasing. The story closes on a victory that feels like a violation, and that is the point.
