I've been playing through Doom 2 using Brutal Doom in gzdoom. I've reached the final boss; however, in BD they seem to have changed the Icon of Sin level significantly. They have made the final boss much more active, shooting fireballs, and given it 40,000 hit points (I posted a couple of screenshots here).

So, I tried loading up gzdoom without BD and skipped to the final level. However, it seems different here too. I distinctly remember in the original, when the rising platform was at the top, the aim was too high to enter the opening in the head. You had to fire just before it got to the top and it took about 3 rockets to beat it. However, in gzdoom, the position of the top of the platform seems lower. Also, if I pump 3 (or even 5+) rockets into the hole, it doesn't seem to bring the boss monster down.

These differences are interesting, but what I had really wanted was just to play the original vanilla final level. I assume gzdoom probably increased its hit points because it has mouse look, which makes it fairly trivial to shoot rockets into the opening and sort of renders the rising platform a bit pointless.

So, what would be the best way to play the original Icon of Sin level, the way it was intended, using gzdoom or another source port?

Bump! Any ideas on this?

It seems it is possible to disable the vertical mouse look in the gzdoom options. Does anyone know how I can load up the original, unmodified Icon of Sin level in gzdoom?

You can try Chocolate Doom.

https://www.chocolate-doom.org/wiki/index.php/Downloads

Ok, thanks for the recommendation. I'll give it a try :-)

Ok, so I think I figured out what was going on.

I was wrong. The Icon of Sin level with the Doom 2 WAD in gzdoom is the original level. But, the issue was that for some reason gzdoom was starting the level with the view not properly centered (could have been due to the way I had saved?). So, even though I had the vertical mouse look disabled, the aim from the top of the pillar was not correct (looking a bit downward). So, I just had to recenter the view on starting the level and I was able to play it just fine without the vertical mouse look. 3 rockets in the brain finished him off, as usual.