It took me a long time to finally make it! Swarm intelligence + hostile champions + badder bosses, with a sniper.
I was lucky to get a projecting bow and a brimstone armor (plate). I don’t know if I’d have survived the burning fist + dark fist combo without it.
I am currently trying 6 challenges. It’s hell. Actual hell. Went for what I think are the 6 easier challenges: Barren Land, On Diet, Into Darkness, Hostile Champions, Badder Bosses and Swarm Intelligence. With mage, wanting to go warlock for the saturation benefits he gets, but the furthest I’ve reached has been leaving Tengu at 15-ish HP. I just needed 1 more healing potion… Dodged every single of his attacks, too. Ig it’s just really hard to beat Tengu with 2 healing pots (had to drink the other few I had to not die, starvation REALLY hurts) and on a +1 leather. Had other good run with better armor, was “ready” to enter Tengu, as I’d already explored every single bit of F9 (actually, I hadn’t, Into Darkness leaves tons of dark spots) but died out of starvation.