Doedre the Vile

I don't remember that fight, other than you go into a tank, something pops out, and you hit the vaaletons button and then it says go talk to sin

edit: To be fair you need to assume 2 things when you hear the name Doedre

1) Chaos damage, a lot of it. Some of it is poison, other parts are not (and curing does nothing :( )

2) Curses, not just normal ones, but buffed-up ones that apply in stacks.

2b) Slowing effects, not just from temp chains (see above) but from other effects.

An amethyst flask with "Of curing" or "Of warding" is a good plan. One of my favourite flasks is the Chemist's Silver Flask of Warding. Buys you some speed and freedom from curses for a little while. Any item that says "Your movement/atk/cast speed cannot be lowered beyond baseline" is also good. An extra life flask is a must.

Stay out of purple circles on the ground. If you can't, mash those curing and warding flasks asap and close in on her.