If either door jams on you, it means Chica or Bonnie have gotten into your office and will attack the next time you open and close your monitor. You can try to avoid the monitor, but this will just doom you to be killed by either Foxy or Freddy. If it's the final hours of the night and Freddy or Foxy are far enough away, then you have a fighting chance, but in any other scenario, it's best to just get your death over with.
If you're on the monitor and start to hear raspy groans, this means not only that Bonnie or Chica have made it into your office, but that they will pull down the monitor and kill you at any second.
Foxy just barely averts this. If you see Foxy running down the hall through your security feed, you have only a second to shut the door. It's possible to hit it, but quite difficult, exacerbated by the fact that you'll probably be panicking.
If you run out of power, Freddy will stand outside the left door, staring at you, as if he's cherishing your last moments. If it's 5 AM, and if the RNG is forgiving enough, you might be able to hold on until 6 AM and survive the night. Any other time, kiss your ass goodbye.
If you don't keep the music box running, you'll start hearing "Pop Goes the Weasel". At that point, make your peace and prepare to meet your maker.
Balloon Boy won't kill you himself, but if he finds his way into your office, he'll break your flashlight, leaving you with no way to defend yourself against Foxy.
Failure to wear the Freddy mask in time when an animatronic appears right in front of you will cause them to vanish...only for them to pop up in your face as soon as you open your monitor or put on the mask. Once you catch on, you can try to avoid using either, but this leaves you unable to wind the music box. Sure, you can still flash Foxy (for as long as Balloon Boy doesn't come close) and prevent the others from attacking by just staying in the office, but eventually, the Puppet will come after you. Never mind that this is quite difficult to avoid in the first place; not only would you have to be very late into the night to survive, but you'd also have to both recognize that you missed your chance to use the mask and avoid throwing it on too late out of reflex.
If you see Springtrap looking into your office from the door, or worse, actually entering the office while you have a monitor up, there's not much you can do except wait for him to get you. Even if you don't use a monitor, the vents will eventually fail, and you'll black out, allowing him to move in to kill you. If you're quick enough, you can save yourself from a game over if Springtrap is looking through your door by triggering the audio in CAM 1; however, if you see him run past your monitor while it's up, then you're dead.
If you see Springtrap in CAM 14 and 15 (vent cams that directly lead to the office) and close their vents, only for him to disappear, that means he has successfully entered your office, and he's going to kill you in a matter of seconds. There's nothing that can be done about it.
If Springtrap is near the office and you get jumpscared by a phantom, you can pretty much give up all hope. The resulting ventilation error will not only force you to waste precious time resetting it, but will also speed up Springtrap and give him an opportunity to sprint to your office.
If you accidentally close a door when no nightmares are nearby, Bonnie or Chica will instantly run to the door and never go away. While it is possible to avoid this if you open the door, hear breathing, then shut it again, most players will take a long time to discover this trick. If you're not prepared, you'll receive a jumpscare next time you flash your light (or if you run away, the next time you turn away from the bed.)
During the Boss Battle against Nightmare Fredbear, Nightmare, or Nightmarionne, they can laugh and enter the room. However, this laugh can also be a fakeout, meaning you'll have to either guess if he's in the room or not or check everywhere. If you're fast enough, you can usually pull this off with no problems on Nights 5-7. On 4/20 however, checking two locations and finding no animatronic usually means that you should just prepare for death, as it's highly unlike you can clear him from the third in time.
Entering Funtime Auditorium twice during Night 3 or entering the Scooping Room during Night 5 will result in unavoidable death from Funtime Foxy and the scooper respectively. Subverted in that neither of these actually lead to a Game Over and are necessary to progress the main story.
Much like the first game, running out of power results in a swift death unless you're very close to 6 AM. While this can only happen during the Boss Battle against Ennard or the Custom Night, it's more punishing; instead of an extended staredown with Freddy, you'll be left sitting in the darkness while the animatronics move around as normal. Ballora will start closing in for the kill (even if she's at 0 AI) and is usually far less merciful than Freddy, capable of killing you in seconds flat.
The cupcake minigame is a Timed Mission, and a fairly strict one at that. Even a string of minor errors can lead to falling far behind, and in some cases, may even warrant restarting the run.
There are plenty of adversaries that indicate that your Hope Spot is about to get crushed before they inevitably kill you, such as Foxy's parts slowly piling up in the office, Toy Freddy's screen having "Game Over", Mangle appearing on your ceiling, Withered Chica being stuck in the vent, Rockstar Foxy saying "Yar, ya win some, ya lose some", and many more.
Occasionally, you reach the point where you know you're dead and should probably turn down the volume of the inevitable jump scare. In 3, for example, once Springtrap is crawling through the vent to your right, it's over.
If the player accidentally spawns a Giga Montynote done by leaving the main stage and returning when Monty is using the search light, which unloads the area this Monty is meant to be trapped in but does not despawn Monty, this Giga Monty will never stop chasing Gregory and cannot lose sight of him, even within Freddy. At that point, you will either be forced to face one of Monty's jumpscares or die to Freddy once he loses power.
Any time you alert one of the animatronics and end up trapped in a dead end by any means. Unless you're right next to Freddy or have the Faz-Blaster or Faz-Cam at the ready, you're pretty much done for.
Hiding right next to an animatronic usually results in them finding your position seconds later. You'll almost certainly be caught if you stay hidden, but jumping out isn't ideal either, as you're very likely to land right on top of the animatronic. Not a good position to be in, and one that very few players manage to escape from unscathed.
At the end of every hour, the power is temporarily diverted to the recharge stations, causing a Timed Mission where you must get to a recharge station before the start of the next hour. While most of these sequences are surprisingly forgiving, the final one tasks you with traveling from Parts and Service to the Pizzaplex's main entrance instead. Due to how expansive the Pizzaplex is, it's easy to get lost and end up way too far away from the exit to escape in time. At that point, you might as well just wait for Moon to find you.
In earlier versions of the game, it was possible to somehow get trapped inside Freddy without the ability to climb out. Whenever this occurred, it was only a matter of time before Freddy ran out of battery and killed you.
Letting Chica or Monty in the control room during the Final Battle with Burntrap was thought to spell certain death for a while. Thankfully, it was eventually discovered that you could still win with them in the room with some very careful movement and a lot of stuns from the Faz-Blaster. If Burntrap manages to hack Freddy though, things won't be quite as easy.
