So each AI got his own pattern that is good, will they always have that pattern or the behaviour will be random?
Random behaviour may cause new elements but also fustration I think while fixed behaviour may not bring new stuff but when the player learns the patterns and counter-attacks them he will have satisfaction I suspect.
You bring up a very good point. In my game, different enemy types have very similar behavior but a different set of skills at their disposal. For example, turtles can't sprint or farmers are "loners" and do not alarm other enemies nearby. So I hope the player will figure that out and be able to predict enemies' behavior, which is fun, I hope.
How will you handle the possibility of "lose more" situations where the player loses and then has an ever harder time to battle the enemy?
The "lose more" downward spiral could become a problem, yes. I hope this is countered by a mechanic I added earlier: In every level, there is an altar hidden somewhere. When the player finds that altar and activates it, the power of all demons is reduced. Also, if a player really wants to kill a specific enemy like a demon, they can buff themself up by sacrificing a couple of materials and get a big advantage for a period of time (long enough to take out that enemy, I hope). One last thing that can always be done by the player is to leave the level and then start it again. The killed (non-quest related) enemies and state whether they are a demon or not is not saved between play sessions. This can be compared to Diablo II, where killed enemies also were not saved and in case you really maneuvered yourself into a situation where you could not retrieve your body (and equipment) after dying, you could leave and rejoin the game and found your body in town at your chest. Not the most elegant thing, but it worked, I guess. But it will need a lot more testing, until I have it ironed out for my game, I guess.
Also, since the demons grow stronger when they defeat the player, is there an story explanation for how the player can come back after being defeated?
I do not address the death of the player story-wise. I love when this is done like explaining it with different time-lines (Into the Breach) or that the player just passed out and was saved by an NPC (Stardew Valley). I am currently not planning to include something like that. Would you say it would be way cooler to have a story explanation, JobLeonard?
Nice! Perfect elaboration regarding AI again. IMHO, AI is weak part of many games even today in 2021, so nice to see such focus on it in your game.

I am happy at least I appear focussed

But in fact I often feel like really wanting to work on something but force myself to improve another more urgent thing. Then again, as solo devs we have to keep it fun for ourselve to not get burned out. A little texture-overhaul is next for me and I am really looking forward to that.
Thanks to you three again. I have not been a member of this forum for a very long time, but it is so cool that people like you take the time to think about other members' projects and give such valuable feedback and criticism.