9 Awesome Hidden Modes In Popular Video Games You Totally Missed

1. Blue Sphere - Sonic & Knuckles

In a revolutionary and never replicated move, Sega released Sonic & Knuckles as a one-off 'Lock-On' cartridge that could actually physically house other Mega Drive carts on top.

Connecting different ones produced a variety of results, ranging from using Sonic 2 and 3 to access versions of those games' levels with Knuckles being playable, or giving you 'Blue Sphere'; a faux-3D collection minigame featuring Sonic and Knuckles.

There were two ways to unlock this - either attach any other Mega Drive cart on top of Sonic & Knuckles and you'd get the first level of Blue Sphere, or do so with the original Sonic the Hedgehog cartridge, hit A, B and C at once when the game presents the "No Way!" message, and you get the full game.

Possibly the finest hidden mode in the history of gaming, actively rewarding players for keeping their physical copies on-hand - something modern studios should actively learn from.