I'll call it "sleeper" for simplicity.

SPAWN LOCATION AND HOW THEY EFFECT EVERYONE ELSE

Sleeper sits in it's own room, no one else goes in or out of it. When it's deactivated, everyone make their normal sound cues because sleeper is not in the building/area. But when active, sleeper sleeps in their room, making everyone's sound cues quiter, and smaller/weaker animatronics move faster when near sleeper's room.

BEHAVIOR

Sleeper sleeps in their room the whole night, unless the player makes noise, INCLUDING THEM TALKING.

If sleeper wakes up, they'll walk to the office LIVE ON THE CAMERAS. They'll send anyone in their way backwards once. When they make it to your door, if it's closed, it'll open up automatically and send anyone at it back to their starting position as well as anyone inside your room. Sleeper with walk in and go through the other doorway back to their room, giving the player a side glance.

UNLESS YOU MAKE A NOISE. Then sleeper will freeze and stare at the player for 2 seconds before walking away.

DEATH

if the player makes ANOTHER NOISE, then they'll grab the player's thoat and strangle them to death for 15 seconds, staring into their eyes as they do it. After one death, if they kill the player again, they'll wait a second apon grabbing them before snapping their neck.

A.I

The only thing that would change is how long they stay in the room as the music swells before sleeper leaves as they'd stand in place at the center of the room for a time, depending on their a.i. level.