The 4 Arenas in Dassero's Dream? I mean....fuck me. I don't know if Mercliess scales up other factors of it, but it was I kid you not, wall to wall enemies.
I didn't get pics of the last arena at full spawn, but, I basically had to enter, hit Abyssal Shout, swing twice with my AoE melee attack, and then die. After doing this 10 or more times, finally, the weaker guys died off enough I had some space to shield charge like mad around the area, throw down Temporal Chains and Spectral Blade for the next 6 minutes, or until my potions would run out and I'd die. What's not pictured there either are the 3 to 4 stacks of Frenzy each mob was carrying around after some of its guys start dying. The last room was 1 Unique and 2 Rare monsters and at least 2 uncommon packs of those archers who stack poison on you. It was the most ball-breakingly unforgiving thing I've seen in this game. Worse that the Dominus fight.
It could be trolling, but surely it's bad design to spawn you into the same spot every time you enter an area, for exactly this scenario. I don't know who this level of challenge is really aimed at, because it ain't the casual player of PoE. It seems more in line for people who play Leagues and have all sort of silly broken gear. I did some casual reading for what it takes to reach Lvl 90+, and it just kind of seems to agree. The XP loss, which is what gives PoE an edge to its gameplay, could make the game almost Dark Souls-esqe in its challenge (now that the netcode is more or less fixed.) But then GGG goes one, two, or three things over the top to just make it a death march to get anyhwere or do anything. At least solo. One of the people that has reached 100 did say something to the effect of "they need to rethink how grinding works for endgame because it's difficult to nigh impossible to pull off solo short of tens of thousands of hours played, without dying."
The unique mob that broke my will to play today was the Bone Queen. At 2000 HP + ~600 ES, a single barb from her aoe spike thing does ~1600 to ~1800 damage to me, with about 55% damage reduction. I don't know if the attack is Physical or Chaos. If it's Chaos I can understand why it's killing me. But if it's physical....fuck me. For how fast she throws those attacks out, I'd need to be several orders of magnitude tougher to even have the chance to whittle her down.