The HOM in the sky appears to be vanilla Doom II's draw limitation. Not sure if it's based on distance only, but I suspect it depends on the amount of stuff that needs to be rendered as well.

It's called "drawsegs overflow". Unlike the infamous visplane overflow, this one doesn't crash the game, but the portions of the screen won't be drawn. In general, you need to cut on the amount of lines visible at the same time, although it's more complex than that.

http://doomwiki.org/wiki/Seg

As far as I understand, visibility checks are only affected by 1-sided lines in this case.

ok, thanks for the info!

I can recommend Chocorenderlimits

for checking your map for vanilla compatibility. It helped me a lot.

I used it for making my map... but that bug still here!

I haven't taken a close look, but if we're talking sky HOMs, if there's a place where you use sky on both the ceiling and the floor, weird results can occur. In particular 1-sided lines will cause HOM above and below them; maybe this is that?

[/random_guessmobile]

Yes, that's the deal with this map! Actually the bugs appear in a part the map where the sky is used only in the ceiling... but the bug still appear...

playing on UV, took me two tries (died to the pain elemental first time). completion was 94%/100%/100% in 15:03. it was fun overall but i would've liked it to be a bit harder--after you got the soul sphere you didn't have to worry about much, and i didn't even use the rocket launcher.

i also think that the opening up of new areas could have been more intuitive. i often hit a switch somewhere and then had to go search the whole map for the door that had been opened.

I liked the doubling back in the first area (including the ending) but once you get outdoors I agree that it wasn't too obvious which deadend opened up when progressing. The huge area with the pit seemed like it was gonna be more action packed but it was a let down. Indoor design felt good though. Love the berzerk tease

Playthrough: https://www.dropbox.com/s/3v6l1hjj5wjfcih/daimon1.lmp?dl=0