On this page of our FNAF Security Breach guide, you will find a walkthrough for Roxy's Weakness mission. Here we supplied a detailed walkthrough for the task.
Activating the go-kart.
After upgrading Freddy in Parts and Service, your next task is to get rid of Roxy. You can find her in Roxy Raceway, an attraction on the second floor of the Atrium. Go through the gate and go to the very end of the technical corridor. This is where the entrance to the attraction is located.
Continue along the corridor until you reach a locked grate - you have to use Freddy to unlock the path forward .
Once inside, go down straight away and head to the right side of the hall. You will find a go-kart there. The driver, however, lacks the head.
The missing part can be found on the opposite side of the hall, in the crates with damaged parts. . . Unfortunately, the head you found requires repairs. The walkthrough for this objective can be found in Repair Robot Head quest page of the guide.
Fighting decommissioned Roxy
Once the head is fixed, you can return to the go-kart and attach it to the body. A cut-scene will start.
When you regain control over Gregory, drive to the decommissioned Roxy and take her eyes. Now, approach the door and press the button. The animatronic will appear in a new form, breaking the door down.
Thanks to the fact you've taken her eyes, Roxy is blind and hunts by sound. Nevertheless, this doesn't mean that she is not dangerous, as she has a lunge attack in her employ.
After going through the door, turn left immediately. There is a hole that Roxy will not be able to pass through - use it. Then, run down the corridor and jump into the hideout. Get ready to leave, as the animatronic will perform a jump, closing her distance to you. Once that happens, jump out of the hideout and run through the door on your left.
Turn left immediately and go through the hole in the wall again. At this stage, you need to use Roxy to open the door for you, As the door is barred. Simply place yourself near the door and provoke an attack. As soon as the animatronic lunges toward you, hide in the nearby hideout. This way the door becomes open.
Final sequence involves crossing a burning room. It isn't that hard - hide in the hideout, wait for Roxy to pass you, so you're closer to the exit than her, run to the next hideout, and so on - keep repeating this until you reach the ventilation shaft that ends the encounter.
Time for an another visit to Parts and Service. The process repeats - when Freddy is ready, it will be 6 AM, and you have to make the decision which exit (and ending) you want to choose/receive.