* CopyProtection: Pirate copies of the cartridge obviously do not have the lock-on slot. This means a huge chunk of content will be unavailable, so even though the game is still fully playable, it's a lot less interesting.
* ManualMisprint: A few of the enemies from ''Sonic & Knuckles'' showed up in ''Sonic the Hedgehog 3'''s instruction manual.
* UrbanLegendOfZelda:
** There tends to be confusion as to why the original ''VideoGame/SonicTheHedgehog'' could not be locked in with ''Sonic & Knuckles''. The two most popular explanations are Knuckles would have dramatically altered the color pallet or that Knuckles gliding on conveyor belts in Scrap Brain Zone would cause the game to [[GameBreakingBug crash]]. Both of which were solved by the famous rom hack ''Knuckles in Sonic the Hedgehog 1''.