In the meantime I got it done
The broken floor got me by surprise, I thought I had to kill the bosses at around lvl 4 and if they fall down I lose.
Anyway, the first time I fell down I killed them both with resourcefulness play and without any left at the end

Now the only hard one missing is Cursed Oasis, but I had no real attempt on it yet, so please dont spoil it

By the way, the Spirit Heart in Disposable Shifting Passages does not seem to work properly. The tooltip states it should affect your fireball damage but it doesnt do that. And the wording is in a way, that I cant even say if it should be higher or lower
