Going back to classic games can be a difficult experience. The forward passage of time leaves technology to stagnate, while the memories attached to those old games can morph in mysterious ways.
Run "build.bat" to assembly the Sonic 2 ASM in order to run the game. Run "split.bat" to split the Sonic 2 binary. The SonEd2 project files for level editing are located in the "soned2proj" folder.
A basic sonic rom base for any hack, featuring knuckles in sonic 1 and 2 combined. To edit the code, I suggest going to http://info.sonicretro.org/Sonic_Hacking_Utilities ...
This hobby-fueled trend can give you a screen break on flights.