Sonic the Hedgehog 2 had gone through several changes over its development process. There are several rejected ideas, level designs, and other things that were left on the cutting room floor. The following details several of these things.
These screenshots are consistent with the content seen in the Sonic 2 AutoDemo, and were most likely captured from that release.
Found in Sega Visions: Issue August/September 1992.
This map was stitched together by a magazine via individual screenshots, and turned out to be quite accurate.
Under Ground Zone
Wheels can be seen sparking. Different life icon. Possible mockup.
Sky High Zone
Prototype screenshots show Sky High and Green Hills using some very basic checkered floors, similar to Sonic 1.
There's palette differences and more trees than in the final game too.
The checkerboard style is used in the opening cutscene, the ending and can be seen scrolling in the title card animations.
Aqua Lake Zone
A slightly different title card, with Sonic and Tails jumping onto a different type of floor.
Green Hills Zone
This image is thought to be a mockup, as far too many sprites are being rendered at once, for the hardware, the boss (and Robotnik) do not appear in this zone and there are a great deal more rings (in addition to the differing HUD).
A later build with final trees, but prototype ground.
Title screen with rearranged copyright information and no ™ symbol.