Dr. Mario (NES)

Dr. Mario is a puzzle game featuring Mario, who throws colored pills into a bottle to match with like-colored viruses and destroy them. It's also been remade several times since.

Unused Sprites
These sprites were intended to appear in the cutscenes shown between levels.



Either a soccer ball or a meteor. Nobody knows.



A snowman in boots? Whatever it is, it does have a proper tilemap and behavior, and its placement in the sprite list suggests it was meant to appear in the Level 20 HIGH cutscene before the final UFO scene was implemented.

Anti-Piracy
The game features a simple anti-piracy check that will intentionally crash the game if the title screen is altered. On reset, the game performs an 8-bit checksum of the area of ROM containing the title screen tilemap data. If the check passes, RAM address is set to  and the game runs normally. However, if it fails, is set to  instead. This address is checked whenever a pill lands; if it's set to, the game pulls whatever value is stored at RAM address , pushes it to the stack three times, and performs an RTS. This causes the CPU to jump somewhere in RAM, and since there's no valid program code there, the game soon crashes.

Interestingly, a very similar 8-bit checksum routine (and method of crashing) appears in Final Fantasy. Perhaps the programmers drew inspiration from NASIR?