Check all cameras often and determine where the critters are.
RNG will determine when most characters activate and some of their movements, but for the most part they will move in predictable patterns. Knowing these patterns will help anticipate their actions and keep you alive. The "Characters" section of this guide details each of the 10 creatures, their starting points, room patterns and office access points.
There are three office access points are: The Office Hallway, The Left Vent and The Right Vent. When a creature accesses a vent, it will make a distinct "bumping around in a vent' noise twice. On the second time, it will appear in your office.
Wind the music box. Wind. The. Music. Box. The music box is a new feature in this installment and is the only way to avoid being slaughtered by The Puppet. Failing to wind the music box means that you have between 5-20 seconds before your untimely death. The music box kindly displays a triangle shaped warning sign when it is running out. Keep an eye out for that.
Some creatures can be scared away from the hallway with the light, but the usually only change direction and head to a different access point.
Once something gets into your office, put your mask on immediately. You will either die anyway or it will leave.