When William was making Nightbear it was designed based off Fredbear's blueprints and was intended to go towards sounds during the day. However due to a error in the animatronics code it has selective hearing. In the case of wanting to go towards the more medium level noises that come from the office. But music(as played from a music box or speaker) will cause it to walk back to its stage.

During performances on the mainstage the curtains on Nightbear's stage closes to prevent the Animatronic from "losing it's mind"(Henry) for a lack of better words from the noise.

Nightbear's deeper shade of coloring was due to William's personal discovery that bears are normally not yellow/orange but either brown(grizzly) or more commonly black(black bear). The name is a play on Fredbear, replacing the Fred with Night. This is due to the animatronics previously discussed black coloring.

The code that makes Nightbear act strangely to loud noises would later be used albeit edited for use in the Puppet's code.