So here's the thing -- the titular Freddy Fazbear himself isn't actually all that scary on his own. It's when you cycle away from his position for a minute and then check back that he brings the fright.
Freddy's tendency to suddenly be staring directly into the camera when you check backstage can be bloody terrifying if you don't realize its coming. In the first game, I found that sudden change to the otherwise static camera images more frightening than many of the actual jump scare deaths.
The Nightmare version of Freddy is even more scary when he shows up despite remaining motionless in his jump scare, as all those extra sharp teeth certainly make an impression!