Blue Sphere (in options dialog as "Special Stage Mode")
The European and North American versions of the collection also include Sonic the Hedgehog The Screen Saver which the player can customize Windows with Sonic themes, wallpapers, icons, and music from Sonic 1, 2, 3 & Knuckles, and the Japanese soundtrack of Sonic CD in 11 kHz WAVV format. However, in Japan, Sonic & Knuckles Collection and Sonic the Screensaver were released separately on the same day.
The gameplay is identical to their Mega Drive / Genesis counterparts, but all of the music is emulated in MIDI format. Some tracks (Carnival Night Zone, IceCap Zone, Launch Base Zone, the Sonic 3 Credits theme, Knuckles' theme, the sub-boss music from Sonic 3, and the Competition main menu) was replaced with music taken from an early prototype of the game. One possible explanation for this is that the final pieces of music from the Genesis version used sound effects not contained within the general MIDI standard, and many sound cards at the time of release did not have the capability to play additional samples along with the MIDI. Another explanation for the replacement is that the songs were replaced due to legal reasons, because connections could be made between similar songs by Michael Jackson.
This game is virtually impossible to play in windowed mode on any system with a CPU faster than 350 MHz, because the game does not have proper speed-limiting routines in this mode. However, the timings used by the game are based on the monitor's refresh rate. Switching the game to fullscreen mode lets the game play properly, no matter what your system speed is. In windowed mode, the game can be played at the correct speed whenever the screen refresh rate is at 60 Hz. Sega has also provided a patch to fix this problem without reducing the refresh rate.
Angel Island Sonic in Knuckles': To do this glitch you need Tails. Have Tails carry Sonic up then stop flying. If you have Hyper Sonic, you can double jump through the dirt. You can skip the Mini-boss if the game is Sonic 3. NOTE: If the game is Sonic 3 & Knuckles you are fighting 2 Robotniks.
Marble Garden Bypass Mini-boss: Spindash in the boss room, but don't go too far. Now Screen Scroll Glitch. The minute you do the Screen Scroll Glitch, Hold right. You just bypassed the Mini-boss! You can also fight Robotnik in a Special Stage Room.
Carnival Night Underwater: Get to the place where Knuckles shuts the lights off. Then have Tails lift the barrier you just went through. Keep on going backwards and... You're in Carnival Night Underwater!