And is it possible to calculate the bonus round wave from the time passed? Because armor is linked to wave count isn't it?
https://mazebert.com/2014/05/18/new-armor-calculation/ That has everything you could ever need to know. Knuperhexe does a linear removal of armor, allowing you to push their armor values in to the negatives (IE, 10 damage could do more than 10 damage on a hit). It is independent of ignore-armor effects.
Well yeah that's what I already know ;) But I don't see the independence from armor reduction it certainly has something to do with it. The question is how.
Imagine Creep has 100 armor, and you have something that ignores 10% and a Knuperhexe that removes 200 armor. The Tower is looking at that Creep as though he has just 90 armor. If he enters Knuperhexe's range, that drops to -110. The two effects are "separated" so to speak. It's not her lowering his armor to -100, and then the tower ignores 10% of that effect, leaving it at -90%.
The results seem to consistently prove it in my game (As I usually have my Dark Forge equipped with the Spectral set, and able to fire both in Knuperhexe's effect and out of it), but if you want a 100% definite confirmation, you'll need: Blood Demon's Blade Knuperhexe Armor-Bypassing Item Ganesha or Manitou Give the Blood Demon's Blade to Manitou or Ganesha. This will give you a tower with an absolute damage number. Place Knuperhexe within range. Compare their damage before an armor-bypassing item and after. I don't have Blood Demon in my current file, so I can't do it and post a screenshot.