I found an optimization in NA which allowed 92% without any ridiculous Jack-O-Chica RNG. ST on the other hand is extremely RNG. I calculated the odds to be 1 in 1026, assuming you reset at 1:00 if Mebird doesn't show up. This doesn't account for Dee Dee though, so the actual odds are even worse. Average completion time is literally like 25h lol. I don't know exactly how long I spent on it, but it was easily the longest so far.
Optimal strategy:
Nightmares Attack (92%)
- Go to cam 2
- Avoid resetting the ventilation at 1.0s intervals
- Get all 4 Mebirds (1 in 4) and select soundproof with fast cymbals on all of them
- On the first three Mebirds, soundproof and turn on the fan when the office hits 90°, then hold it between 60° and 61° when soundproof ends
- Leave the temperature at 70° around 3:35
- Get fast cymbals at 3:54 or later, then click Mebird at 4:00, shut and open a vent to skip Rockstar Foxy's voice line and select soundproof
- Shut both doors for about 0.4s when the office hits 99° around 4:04
Springtrapped (103%, depends on how many Mebirds you get)
- Go to cam 3
- Afton takes 1.1s to attack
- Get as many Mebirds as you can and select +1% on all of them