I attempted the Shadows of Yarnum fight yesterday. I happened to have a co-op NPC companion with me at the time I did the first run. A complete coincidence, since I had no idea there was a boss fight coming up. During that run, I had defeated one of the enemies, had one down to a tiny sliver of health, and the final one down to a tiny sliver of health. The giant snakes popping up out of the ground was unexpected though, and they killed me pretty fast.
Then knowing what I was up against, I brought out one of the 20 Madman's Knowledge in my pocket to gain insight that I needed to summon this particular NPC. It tasted squishy, and I would have preferred it cooked, but there's never a time when brains are not delicious, so it was tempting to eat more than one at a time, but I resisted.
Unfortunately my 2nd, 3rd, 4th and 5th runs were much less productive. On some of them my NPC companion died and then the three made quick mincemeat of me. On some of them I got tangled up in flame, other times I got sliced and diced with a vengeance. So I took a break.
This morning I decided to try the run solo for the first time, and get some practice in. I only had 14 Madman's delicious brains left, after all. The solo runs were an absolute disaster. I even watched a couple of Youtube videos of other people doing it solo. One guy relied on his gun to do visceral hits only. Another one killed the fireball guy first to get the ranged attacker out of the way. Another one got rid of the main sword guy first. But in all cases, I didn't really understand why they weren't getting swarmed while attacking one of the three. The other two just missed or stood around obligingly for long periods. In my attempt, all 3 of them were coming after me pretty hardcore all the time. If I ever attacked one, I'd get hit and interrupted by one of the other two. (Also I noticed that people's health bars in these videos tended to be at least twice as big as mine, so they're doing this fight with a LOT more vitality than me).
Anyway, I decided to try it co-op again, and my NPC coop buddy kept the candle-holder occupied, and that was enough for me. I made quick work of the swordsman while dodging flames, and then brought down the fireball guy too. And by then my buddy had the flame thrower/sword guy down pretty low and I finished him off.
Bloody good cooperation feels satisfying I tells ya. I'll continue from that lamplight later tonight.
I am a tad worried though, that only having my vitality around 19 is maybe going to be something I regret now that I'm nearing level 50 and the levels are each getting pretty expensive. I just thought going Endurance heavy was very useful early on.