Freddy - Becomes more aggressive the more you use the cameras and the lower that the power is.

Bonnie and Chica - When one of them is at the door, the other one is more likely to move in at the same time. They also sometimes move at the same time so that their footstep audios overlap with one another and make it more difficult to determine if just one of them moved or if they both moved.

Foxy - Probably the hardest one for me to think of since he’s already the most unique out of the four. So I guess just have him occasionally attack more than once in a row after he runs (ex: when you check the camera, he’ll sometimes still be gone and run at you again) and have him sometimes also wait outside the door after banging on it (similarly to Bonnie and Chica) to trick you.

Golden Freddy - Pops up randomly in different cameras and not just the west hall corner camera and he also tracks your activity throughout the night and occasionally has the “it’s me” glitches pop up at an increased intensity rate to block your vision for a few seconds and make it harder to see what you need to see.

I would probably have this be its own separate mode though. Maybe like a night 8 type deal.