several undead dolls exploding on you at once is more or less the only thing that can insta kill you, so I pretty much just dont go where they can spawn (with the exception of throne)

Personally, when doing abaddon, icy cellar or throne I will never teleport ahead blindly. Usually I'd throw a deathmark first, see if monsters aggro to it, then teleport to my deathmark spot, repeat. Only becomes safe to teleport if you've seen 3 types of non-doll monsters so you know they aren't chosen. Although I guess 2 melee non-doll packs being chosen also excludes dolls since there's always 1 ranged pack, but I CBA to figure that out during a run.
If you feel like clearing swampy pit / flayer dungeon, its pretty safe to do so by just defusing every room with deathmark. You have so many walls to protect you while you deathmark your pack ahead of you and the room clears instantly
I did both those dungeons all the time and as long as you're playing cautiously its no problem

But there's no reason to set foot in durance, since its totally unrewarding. Its not whatsoever worth teleporting to meph

What modifications would you make for hardcore ?

i played this on hardcore and all variations, just slam a coa in the helm, and use obsession that was enought i even used a coa with facet + colossal jewel

Rest of your gear?