This is a neat little trick I discovered that uses the OilOcean's graphics to 'patch up' some of the floors and graphics inthe unfinished Hidden Palace level:
You do this trick exactly the same as the Hidden Palace hack,except you take the initial snapshot of the Oil Ocean zone,rather than the Emerald Hill zone.
After doing the hack and killing Sonic, you will enter the HiddenPalace zone again, except this time it will have Oil Ocean'sbackground. Use the debug and move around the level. You willnotice that some (not all) of the floors have been implemented,using Oil Ocean's graphics!