What mechanics or aspects about it would you say made it scary? Perhaps include some examples and explain its shortcomings as well.
Not a sidescroller but it dealt very well with limited technology back in the day. Silent Hill 1 for Playstation. You could draw some inspiration from it, the scary barely visible scenery, scary situations with and without violence, etc.
Currently speaking I don't have the time or resources to play the game, much less get a playstation.