"Once upon a time, I tried to backport a "Carnival" level from Redux into original Postal, since it was one of the wishes from RWS for a possible update. I managed to prepare all the stuff but it seems that the actual compiler is uncompleted, it can't build a level with huge amount of layers. It can compile some simple levels or with small amount of layers, so I assume there's some sort of limitation that can be somehow tweaked. I tried a lot of workarounds, but still no luck, so I dropped the "Carnival" backporting. Here's a showcase of one of my last attempts to make a custom level for POSTAL 1. At least something that looks fine.

If you wish to make your own level, read this guide. But read it VERY carefully, because one wrong step can ruin your progress. Also I wonder if there's any experienced folks who can look into this Python script and change it into something that will work without any problems. If you did - please, let me know. Thank you.
https://steamproxy.net/sharedfiles/filedetails/?id=2726139546"