The Hard Mode was added into the game to give it some more content, that way more replayability would be there. However, the game was quite slow, and this was due to it being more of a story-telling game though the cutscenes. Even some of the mechanics returned for the old Golden Sonics from the other games, which made it interesting to figure out, or a cool experience for the older fans. On top of that, every Golden Sonic from the series came back all at once for a crazy nostalgia trip for the old fans of the series. This game was worked on the most out of the 5 FNaF-style games that FNaS had in its canon.
The fifth game in the series, which due to not being based on any FNaF games, was pretty much completely thought up specifically for that game.