At the end of chapter 2 when we killed mommy long legs she says "He'll make me part of him".

but who is he??.

a monster hand comes out and grabs mommy into the darkness.

it's a metal hand with spiky fingers.

I'm assuming it might be a monster which is also collecting other monsters and their body parts.

I'm assuming we will see Experiment 1170 and mommy again, but this time they'll be apart with some spiders.

And, this is kind of like FNAF Security Breach's blob.

If you look back to the tape it's said that an experiment almost escaped and it could be possibly taking things with him.

The experiment could have been killing people too, then that's why using bones on his own body.

I mean we've already seen human bones on him, so this is probably true.

On top of that mommy long legs also killed The rabbit from musical memory.

Since she's a perfectionist she wouldn't have that Experiment 1170 and the rabbit go.

If you adjust the camera settings you can actually look around and see them hanging around

to go into more details the audio file names in the game are actually named of her killing the rabbit and mini experiment 1170's.