1) definitly rink of frozen blood. hate it, hate all of it, it makes me angry, especially tha ladies with their robes and warhorns, calling wolves.
2) ingenious cistern. i like it, the stone pillar mechanics as well as the stage endboss, he just melts down in one go, its just satisfying.

But i have to add something: with the recent texture bugs i hate seht's balcony and spiral shadow more than anything else. in Balcony you cant see ANYTHING other than the enemies. sounds not so bad, but its really hard to navigate arround the pillar in the middle, while avoiding invisible AOE...in Spiral shadows, the glowing pillars vanish sometimes, what makes it hard to tell if the little spider bumhole just webbed one or if its free.

Argonian poison stage, either RNG kills me while the boss is doing his roar thing, or I'll get poisoned as I kill it so can't cleanse and die.

1) Stage 5 - Ice Rink is painful at times, normally adds mostly as they are quiet hard hitting unless you burn them quick. Stage 7 is a pain at times with the RNG element I encounter at times. Stage itself is not hard, but if there is one that stops my flawless runs, it can be that one if its not stage 5.

2) Stage 1 (or does that not count ), aside from that, Stage 8 - igneous cisterns is pretty straight forward and a fun stage, almost a relief stage between 8 and 9 IMO.