Tips for Furfur?

[Kalil]

I've downed the other five black page bosses and the boss of Tanis, but can't seem to make any progress against the Duchess. My usual strategy of 'have 2x white rose pacts set them on fire until they stop squirming' doesn't seem effective. As soon as she starts spamming Fall, it's over in two or three rounds, she can one-shot my soul clarity 40 peer fortresses...

[ウィッチ（？）]

Guard her attack till she weakens herself about 4~5 times (if you cannot survive her attack here, then better come back later).
Once she is sufficiently weaken herself, then start pounding her with everything you have (prefer with high donum attacks) before worst can happen.

[KLightningflik]

Bit of luck involved. Once she's done weakening herself you'll want to use your best attacks to try and take her out before she uses her overlord abilities. I got lucky with Gore attacks. Make sure you're raising your soul clarity too.

[Kain Yusanagi]

Use attacks that afflict poison, and use Gothic Coppelias for increased chance to gore.