So I walked into Halls of Torment without reading about it before going in, and I have to say being located on the opposite side of the world from the server made Lyris Doppleganger a lot harder than it should have been.
For one, Elder Scrolls Online’s controls aren’t exactly responsive to begin with. For another, the lag means where she’s facing and where she fires her fork attack can be very different angles. Third, dodging the fork itself is very difficult due to rubberbanding. Fourth, the balls didn’t seem to heal at long range for some reason. I had to kill them while standing close to get a heal. Suffice to say it took me a lot of tries to get this done.
Her first form was easy enough. Melee attacker susceptible to CCs means CC and kite her.
Her second form is ranged with a fork attack that has no tells and goes off at variable angles so that got problematic. I eventually settled on a plan to reserve all Magicka for keeping her CCed with Shattering Prison (Encase).
For damage, I used DoTs from Poison Arrow and Acid Spray (Arrow Spray) to whittle her down, on top of spamming normal attacks of course. I kept roughly 33% of my Stamina in reserve for sprinting. The healing balls were handled with normal attacks.
Having 1,000 to 1,100 HP worked well enough to account for mistakes.
Long story short, CCed and kited her. Full video follows.