Horizon Zero Dawn ended with Aloy defeating HADES, a corrupted AI who believed its purpose was to wipe out all life on Earth. To do so, HADES planned on reawakening a group of robots, known as the Faro Plague, who were responsible for ending the world originally. Aloy was able to shut down HADES and prevent it from enacting its protocol.

Horizon Zero Dawn's ending shows Aloy defeating HADES and shutting down the signal that would've restarted the Faro machines. Seemingly victorious, she travels to Dr. Elisabet Sobeck's home to remember her past self. However, after the game's credits, a cutscene begins that shows a red energy emerge from HADES' core.