Baldur's Gate III

Upon defeating the Netherbrain, the player character would be given two final options that would decide the fate of Baldur's Gate: Either command the elder brain to destroy itself along with all the mind flayer tadpoles that were implanted into its victims, or dominate it and become the Absolute in charge of an army of mind flayers and tadpoled thralls ready to conquer the world.

Example of:
Last-Second Ending Choice