Tadas

A very strong and well rounded party is taking first four people you meet - Eder as tank, Xoti as priest, Aloth as wizard and Seraphen as cipher. You have all roles covered and you can choose freely whatever role you want to pick for yourself.

Some more thoughts with more testing. Borrowed instinct does not stack with the chant both get same acc bonus, though only borrowed instinct shows up with moseover, (however same amount on the roll). Also doesn't stack with devotions of faithful. Marked prey does stack. She has low crush armor 11 vs everything else at 17. I think I bugged her out on my first kill (or maybe I was standing just out of range with my tank), because he didn't get wounds. Or maybe chance to wound is related with her accuracy. Positioning is not that important, it seems they spawn random number of melee and ranged spiders. Melee gets crushed by boss, but after you achieve a limit no new spiders spawn (unless you kill some of them yourself). It seems best way to tank her is either with summons or just position where she can't reach you with melee attacks, not because of damage, but her consume has a chance of additional effect that causes you a wound (though you can clear those with luminous adra potions). Getting 16 armor vs piercing is great on tank, her normal attacks have 15 penetration. And 9 vs piercing on rest for crystal-eater spiders (they have 8 pen).

I killed her on Potd upscaled by positioning my party near entrance, she blocked new spiders coming so I could manage how many stacks she would get. Everyone before the fight ate shark soup, except my seer - I put on her armor that made her immune to dex afflictions. I gave her 2 weapon pen food. I stacked all ranged accuracy items on my seer - helm with +10 acc against beasts, ring with + 4, gloves with 25% missed to grazes, potions, weapon with -20% reload time, but with +2 pen and +10% dmg etc. I managed to get exactly 17 pen - as much as boss needs to break even. The setup was - chanter was singing +30 acc and +30% dmg against beasts song, and +50% healing. Tank well.. tanked and healer healed. Seer would use borrowed instinct on nearby spider for another +20 acc. I choose seer because she can get most accuracy in game with hunters mark and her passives. Used ghost heart subclass for ranger, because I doubt I could keep pet alive and didn't want the penalty. So basically all I did was - refreshed borrowed instinct on spiders, kept my priest stocked up on heals with ancient memory, kept drinking potions and just shooting. I limited spider kills to about 20, so I had 20% chance to hit with seer. I was afraid that I could not keep my tank alive if I killed more. It took me a long time (after the fight seer done over 10k dmg, but that included some from killing spiders). Towards the end of figtht I discovered an extermely cheesy tactic - salvation of time extends duration of ancient memory too - meaning you can spam it. I put y pallies lay on hand on everyone for heals and setup ai so all my priest would do - just spam ancient memory. For some reason it did not extend time for borrowed instinct, but it made the fight much faster. The extra cheesy part is (I didn't use it) - I think if it extends barring from deaths door duration - you could make party invulnerable.