Sega Genesis Collection - Sonic The Hedgehog Glitches (PSP)

In the game, Sonic has to prevent Doctor Robotnik from collecting six of the Chaos Emeralds in an attempt to rule South Island. He must traverse six "zones", each comprised of three stages or "acts", until he confronts Robotnik for the last time in the Final Zone. The gameplay centers around elements that exploit the increased performance of the 16-bit console over its 8-bit forebears. It is notable for being both simplistic and engaging for players.

At the time of its release, Sonic the Hedgehog was one of the fastest platformers that had yet been released. Sonic could run, jump and roll at significantly higher speeds than most platformers of the time. Unlike other platformers, the game's levels were designed to encourage the player to progress quickly. Springs, slopes, high falls and loop-de-loops were all available to both boost and challenge the player to reach high speeds. This was all accomplished without any slowdown in framerates, adding to the experience. (Wikipedia)

Glitches

Early unlimited lives:
Enable "Level select" and "Debug mode" codes. Put a lamppost just before the sign at the end of the level. Press B to transform back into Sonic and hit the lamppost. Get out until the lives read "1" at the bottom of the screen. Spin the sign to end the level. Wait until Sonic walks out of the screen. Enter debug mode and go under the sign to get out again. The "Game Over" message will appear while the credits are being shown. You now have unlimited lives.

Secret underground hideout:
Enable the "Debug mode" code. Go to the end of Star Light Zone Act 1 without passing the sign. Press B and go under the floor at the end to find a secret underground hideout.

Endless bounce:
Enable the "Debug mode" code. Go to Green Hill Act 2 and find the location with a spinning wheel, two or three falling blocks, and a floor of spikes. If needed, use "Debug mode" to find this area. Make all the blocks fall and land on the spikes, but away from the land at the end of the blocks. You should lose all of your coins and bounce forever until you reset. Debug mode is needed for default invincibility. For an alternate method, get all the Chaos Emeralds for invincibility for spikes enemies, etc.

Cannot move:
Enable the "Debug mode" option. Collect fifty or more rings (or just transform in a ring and get fifty or more). Go to the end of the level and do not pass the ending sign. Press B button and look through your transformations. You should find the Big Ring (at the end with fifty or more rings) in your options for transformations. You can now place another Big Ring. If you place a Big Ring before you pass the sign and behind the sign then go inside the ring the game will glitch. You cannot move (including using Debug mode), see yourself, or hear yourself. Note: This was done in Green Hill Act 1;


Here's 14:45 speedrun of Green Hill: