I didn't make it to the boss. Most of the time I either ran out of stamina or got taken down by clusters of enemies I couldn't handle. I played around 7 runs or so, and I think I was three upgrades away from maxing everything out. I don't recall seeing any sign that I was about to reach the boss. With the current build, those enemy clusters seem impossible to handle. In my latest run, I had to face 4 enemies on the first floor, and there wasn't even much open space for me to move around in.