The main problem is that on the second level, if you enter it normally (by completing the first one, or by a ctrl+l cheat, or whatever it is), not by making the game start you right away at it, or if you die on it, the game crashes with this error:
I tried various things to stop the game from crashing the world and making black holes, like changing different parameters on the custom EXE, like making it the dungeon, turning off finishing the level by dropping into a pit, and some others, and the only thing that worked is by playing the original exe, but that's not the way the mod is intended to be played. So, I probably won't resume the work until I can solve this problem. If it's a common problem, I'd like to see a solution.