Re-released the game again and removed many bosses from the final level. Now there should be more than enough ammo and 1-ups to defeat all the bosses, but I managed to beat it on the highest difficulty (a bit of cheating, repeated saving and dying involved).
Apparently I didn't learn my lesson with Totenschloss (putting a gajillion soldiers into one room), so I ended up taking it up to 11 by putting in all those bosses. If I remember correctly, the final level in WSJ's 'Eisenritter' had a lot of bosses, which I took inspiration to make this level. Nevertheless, wouldn't want you to ragequit like with Totenschloss, would we?
The next Anvilstein fangame will probably have a much sparser enemy count and more spacious levels to fight in. One of my first ideas for new features was to include some sort of stealth mechanic, maybe make the knife more useful and add a suppressed gun. The rifles will probably return from Totenschloss. If you have any other features to recommend, I'm all ears.
Given the game's extreme proneness to crashing, I just looked up the Game Maker forums and found that Windows 8 doesn't run GM8 games well unlike Windows 7 due to the incompatibility of the former's DirectSound with GM8's internal audio engine (not just my game, tons of others as well). The two ways I can circumvent this is to either try an external audio .dll and keep the GM8 format (more feasible) or port the entire game to GM: Studio (which involves rewriting a lot of code and converting files) with its W8-compatible internal audio engine. Which really sucks since I could enjoy running GM games on Windows 7 without worrying much about crashes (and Microsoft is unlikely to update W8's DirectSound, and Yoyogames gave up GM8 for Studio). In short, it's gonna be a bit of a development hell from a technical perspective.
The most far-fetched idea would be to port everything I've made to SDL, ECWolf or not. That will need to be done entirely from scratch.