30 years and we're still finding out things about the game that made the NES famous.
http://www.nintendoworldreport.com/news/42586/new-error-found-in-super-mario-bros
Despite its age, new secrets are still being found in Super Mario Bros. - including code errors.
According to a source code disassembly performed last year and published at The Cutting Room Floor, the behavior of Spiny eggs is not as intended. Rather than dropping down, the eggs were meant to be thrown at an angle based on Mario and Lakitu's position and movement speed, as well as having physics for bouncing off pipes or blocks.
The TCRF talk page indicates that a single, misplaced variable caused the error.
A side by side comparison can be found below:
The existing behavior seems easier to understand/predict so more friendly to the player. Totally possible they nerfed it on purpose without removing the code in case the decision was reversed later.
I wonder if this was really a bug or conscious decision? (Since they are saying it's a bad variable, probably the former. I'm too lazy to look into it.)It's tough to say. They did seem to want to make this game accessible to everyone, so I'm sure they didn't want it to be too difficult. However, the unused behavior is how the Spinies behave in subsequent games, so I'm not so sure. Plus, they could have used this for the "second quest" where Goombas get replaced with Buzzy Beetles and all enemies move faster.
