[Updated on September 26, 2024, to revise outdated formatting and improve readability.]
You can’t really fight The Mimic in Ruin. Right away, the real Gregory tells you to run from the robot through the radio. If you choose to confront the machine, you will get a game over. As a result, you can’t beat The Mimic in FNAF Security Breach Ruin.
Your only option when you confront The Mimic is to run away. Run through the tunnels beneath Freddy Fazbear’s Mega Pizzaplex to escape from The Mimic. You will hear the robot’s feet bounding on the ground as it chases after you. Gregory will warn you that the machine is nearby. However, you can look back to see how far away it is from you. Usually, it won’t be too close to you. But don’t stand in one location for too long, or it will catch up.
The tunnels are a maze. Your best bet to navigate through is listening to Gregory’s direction. He will lead you to the game’s ending. There are three potential endings to FNAF Security Breach Ruin. One of the endings shows The Mimic seemingly getting defeated.
The ending depends on how well you follow Gregory’s instructions in the finale. You will get the Scooper ending if you complete all the minigames and turn left after spotting the green rocks on the floor. The Scooper ending has Cassie making it to the controls room and active the Scooper. The Scooper then grabs away The Mimic.
You get the Normal ending if you follow Gregory’s instructions exactly. The Normal ending has Cassie reach the elevator. You gain the Fazbear ending by finding the Freddy cardboard cutout near the green rocks and putting on the Vanny mask.