Here's a crude PAR level code if anyone wants to skip around. It's crude because once its activated the level you're in will screw up. Either die or go through a pipe after activating and the next screen will be your level, though you seem to spawn at inconvenient places often. Again, pretty crude.
ff0116:00xx
00 = first level
01= 2nd level
02 = Castle
03 = first level pipe
04 = pipe from somewhere, forget
05 = castle 2nd part
06 = first boss
07 - 4th level
08 = 4th level pipe
09 = flying bonus area
0a = level 5 ice cave
0b = level 6 cave
0c = level 6 in front of goal
0d - last boss
No other slots have anything it seems
Was hoping for hidden levels!