Blue Sphere Plus is a Sonic & Knuckles hack. It is based on the Blue Sphere Standalone ROM, with new features, such as: - Pressing B or C now cycles between Sonic + Tails (blue + orange bumpers), Sonic alone (both blue), Tails (both orange), Knuckles + Tails (red + orange bumpers), and Knuckles (both red). - SRAM support to remember the character you last selected, and the last level completed. - If holding A while pressing Start to start a stage, the player starts all stages from then on at top speed (not saved between sessions). - You can now press Start at the first screen to reach the menu, instead of holding A + B + C. - Select "SONIC 3K" on the first menu, and you will play through all 16 of Sonic 3 & Knuckles' Special Stages in order, including the 2 "secret" ones. Saving and code entry are disabled while this mode is active, and the game will reset upon completion of the last stage. - Can Lock-On to other ROMs, including the Sonic games that would normally enable special modes when locked-on to Sonic & Knuckles. - Users can lock-on a file containing custom levels to play.