Endless Mine is the fifth and final Zone in the Competition Mode of Sonic the Hedgehog 3.
Possibly the most popular Competition Mode Zone of Sonic 3, Endless Mine is a mine Zone with some characteristics from Sonic the Hedgehog 2's Mystic Cave Zone and Hidden Palace Zone, and Lava Reef Zone. One of the important features is the necessity of rock breaking in one area to win the race. The tracks also overlap each other, doubling the length of the course.
||While visiting this old mine shaft, use your Spin Dash attack to smash rocks in order to clear your path.
— Sonic the Hedgehog 3 US manual
Using debug mode, it is possible to fight a very glitched version of the Marble Garden Zone boss in this stage. It is done by using debug mode, playing the Gumball Machine Bonus Stage, then exiting with + , going to Special Stage 2 on the level select, and this will screw up the game a bit more, and allows you to do this. It is not known why the extra step of the Gumball Stage acts in this way, but it seems to remove the canvas limit to the right, placing you on a random position.. If you manage to beat the boss, the game hangs up and the Angel Island BGM starts to play. This is the glitch in action.