MemesNBeer's guide is fantastic, I was however able to use another strategy to finish aggressive nightmare mode. The video is all achievements and below that is the written guide I made up for it.
This video is an all achievements playthrough of Five Nights at Freddy’s 3 performed on Xbox One. I am going to preface this walkthrough with the following: This game is a relatively easy 800 Gamerscore, however, if you want the completion it becomes significantly more challenging. This challenge comes in the form of aggressive nightmare mode. A single mistake during the night will likely cost you the run you are on, though not always. Let us begin the walkthrough!
Firstly, the animatronics.
Phantom Freddy, you can pretty much ignore him the entire game. If he starts walking by your office make sure you do not stop and stare at him or you will be jump scared and cause a ventilation malfunction.
Phantom Foxy, shows up in your office randomly after spending time on the monitor. To find out if he has appeared in the office after lowering the monitor move the camera left enough that you can see him but not get jump scared. To make him leave pan right and bring up the monitor again.
Phantom Balloon Boy, occasionally shows up on the camera while looking at the monitor. If you see him on a camera immediately switch to another camera to avoid his jump scare.
Phantom Puppet, only shows up on CAM 08 if you spend too much time watching it. If you get caught by it you will be stunned in its animation for around 15 seconds. To avoid it’s abilities limit the time spent on CAM 08 as to not trigger it.
Phantom Chica, only shows up on CAM 07 on the screen of the arcade machine. Much like the Phantom Puppet avoiding her is as simple as limiting the time spent on CAM 07.
Phantom Mangle, Finished the entire achievement list spending roughly 30 or so hours doing so and did not know she was in the game. Appears on CAM 04 and behaves just like Phantom Puppet and Phantom Chica. CAM 04 is basically never looked at so she will not be a problem for you.
Springtrap, the only one who can “kill” you. He has a relatively simple AI during nights 1-5, he will move from room to room (or the vents) and make his way towards your office during the night. You must use the camera and audio system to keep him occupied in other rooms to finish the night. Some interesting points about Springtrap:
1) At the start of a night he spawns in CAM 07, 08, 09 or 10, look at these CAMs first to find his initial position.
2) If he gets to CAMs 05, 04, 03 you will hear a tone indicating such.
3) The tone from above gets noticeably louder when he enters CAMs 02 or 01.
4) Springtrap only ever moves into adjacent cameras at a time. I.e. CAM 09 to either 08 or 10 but not from 09 to 07.
5) On top of moving to adjacent rooms, he can also move into adjacent vents as well. I.e. CAM 09 to CAM 11 (the vent in the same room as CAM 09).
6) Springtrap has two locations (except vents) he is visible in on each camera. I.e. on CAM 09 he can be seen full bodied in the back or up front where his eye is clearly visible.
7) If he is visible in the window of your office quickly audio cue in CAM 02 then CAM 05 to move him away.
8) If he is visible in the door way to the office audio cue in CAM 01 then CAM 02 and so on.
9) On later nights moving him away from the office door is an unlikely strategy to work. However, if it is 5AM put your controller down and stare at him. You may be able to let the night end without him attacking you.
Repairing Systems: When a system goes down, audio, cameras or ventilation fix them with the following priorities: audio, ventilation, cameras.
If you have multiple systems down and you know where Springtrap is then you should audio cue him into a further away room and then fix one system, then audio cue again in the same room to keep him there. If your audio is down fix this first, then audio cue a room where he will go and continue fixing systems.
This strategy applies to all nights, take note that you should not use the repair all function as this eats up precious time you do not have on later nights.
Night 1. Nothing happens here, learn the controls of the game and explore the layout.
Night 2. Springtrap is now active, however he will move very minimally and is easy to manipulate this night. Find his initial position and track him as he moves. Try and keep him up by CAM 09 and 10 as this is a dead-end hallway. This night is very mild and most of the phantoms should not be problematic.
Nights 3-5. This is where the game’s difficulty ramps up. More phantoms are active and Springtrap will start moving more and using vents. This this the first night where we will employ a strategy to beat the night. First find where Springtrap started i.e. CAMs 07, 08, 09, or 10. If he starts in CAM’s 08, or 09 lure him to CAM 10 and close the vent in that room (CAM 14). When he eventually moves into CAM 09 send him back to CAM 10. Pay attention to the sounds indicating Springtrap has entered a vent. If you hear this and know his last location check the associated vents first. If he is in it seal it if it is not already. If keeping him in the 08, 09, 10 hallway you only have two options as to which one he is in. If you know that one of them is already sealed immediately go to the one that is not first. Continue this process for the night.
This strategy in combination with the tips I gave at the start will work for pretty much every night. The only things that change are the frequency that Springtrap moves, the frequency of phantoms to show up and the frequency that systems will fail.
The Phantom Puppet will become active on night 4.
Starting on night 5 and every higher difficulty night hereafter the audio system will fail after using it twice. This can make things difficult especially when Springtrap is closer to the office and you need to reboot it. Timing and efficient use of this system becomes incredibly crucial. If at any point you lose track of Springtrap, quickly go through each camera and find him and seal the nearest vent. Try to lure him back into the 08, 09, and 10 hallways afterwards.
Night 6. This night is where we start to shift gears in how we deal with Springtrap and the phantoms as they become more aggressive. The same strategy from nights 3-5 can and should be employed for as long as possible. However, if Springtrap either escapes the hallway and gets to CAMs 07, 06, or 05 or he starts in CAM 07 we will employ a new strategy. The strategy
: If Springtrap makes it to or starts at CAM 07 immediately seal the vent at CAM 12. We can not stay on CAM 07 for too long as Chica will eventually jump scare us. Ideally you will get to a point where Springtrap is at CAM 06 and this is where we can begin a loop where Springtrap basically walks in circles for the entire night. If he is at CAM 06 keep the monitor open and follow this pattern:
If Springtrap moves and you hear the CAM 05, 04, and 03 sound, immediately audio cue in CAM 06 to bring him back.
If he moves and you do not hear the noise, he has moved to CAM 07, this is what you want.
If he moves to CAM 07 wait 3-4 seconds, if he comes back to CAM 06 sit there and wait until he moves again and repeat the cycle.
If you wait 3-4 seconds and he has not come back, he is at CAM 08. Audio cue in CAM 07 quickly and return to CAM 06 as to not trigger Chica.
Repeat these steps and make it through the night.
On rare occasions he will go from CAM 08 to CAM 09 quite quickly, if this happens you have two options. Lure him back to CAM 08 and 07 and go back to your loop or proceed to use the night 3-5 strategy.
It is 100% viable to keep using the 08, 09, 10 hallways to finish the night. I personally found that the combination of both the night 3-5 strategy and this one led to my success.
Repair your systems as needed right after you use an audio cue to distract Springtrap. After repairing immediately audio cue the camera Springtrap was last seen/known in to keep him there. Pick up where you left off and continue the loop.
Aggressive Nightmare. Oh boy here we go, the most difficult night of the game. I did this run only using the night 6 strategy of keeping Springtrap in the CAM 08, 07 ,06, and 05 loop. This run requires nearly no mistakes and absolutely no ventilation errors (also a wee bit of luck). The moment you have a ventilation error Springtrap comes for you as fast as he can. He once was at CAM 10 and I got caught by Phantom Foxy, by time I repaired the system he was staring into the office from the window (he will use vents insanely efficiently).