Blue Sphere

Summary

Blue Sphere, referred to as Special Stage Mode in *Sonic & Knuckles Collection*, is a hidden video game embedded within the *Sonic & Knuckles* cartridge for the Sega Mega Drive. It can be activated by inserting any Mega Drive game cartridge (excluding *Sonic the Hedgehog 2* or *Sonic the Hedgehog 3*) into the Sonic & Knuckles lock-on port. Blue Sphere features a series of Special Stages, created using the same style and engine as those found in *Sonic the Hedgehog 3* and *Sonic & Knuckles*. When the original *Sonic the Hedgehog* cartridge is locked onto *Sonic & Knuckles* (including the *Sonic Classics*, *Nick Arcade*, and *Simon Wai* prototype versions of *Sonic the Hedgehog 2*), the complete Blue Sphere game becomes available with all its stages. Most other cartridges will only grant access to a single stage, determined by the ROM header of the attached cartridge and the corresponding stage code in the full Blue Sphere game. Cartridges with especially large ROM sizes (such as *Phantasy Star IV: The End of the Millennium* and *Super Street Fighter II: The New Challengers*) will bypass Blue Sphere and instead launch *Sonic & Knuckles* normally. Likewise, connecting *Sonic & Knuckles* to another *Sonic & Knuckles* cartridge will also result in the game loading as usual.

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