I'm well aware it is absolutely possible to record demos of nonstandard stages (Such as NAGZ, MKBZ, and the Special Stages, among others), I've used the
SRB2Net Launcher to record demos of NAGZ. I'm not sure how you go about it through the ingame console, but if you're using manual commands, you type in these paramaters in under "Manual Parameters" in the Main Options window as follows before launching SRB2:
-file srb2.srb -warp xx -recorddemo demoname
Replace xx with the map number you wish to warp directly to (Consult
this guide here for a full list of SRB2 levels, and
this guide here if you're recording for a map with a letter in the map number, such as Map AK), and demoname with whatever you want to name the demo (note, you do not need the .lmp extension at the end, the game will add it for you).
If you make a mistake during the recording, simply quit the game and try again running the same parameters. If you use the same demo name as the previous recording, the old demo will be overwritten and replaced with the new one.
Once you're satisfied with the demo, you should play the demo back once, just to make sure the recording doesn't de-sync, you can do that by opening the console in SRB2 and typing in:
... where you substitute demoname for the name of the demo you just recorded (.lmp extension not required)
Remember, you have to complete the level at least once with any character in standard SRB2 Single Player in order to be able to warp there.
