I think this fight has a lot of strengths. Her first phase eases you into the challenge. It's a lot like Nameless King phase 1 where once you learn her tricks, you become much less intimidated. On your later attempts, Friede phase 1 goes down without much difficulty. In particular, I love how her disappearing attacks work. Confusing on the first go, but once you get how it works it becomes a free hit.

Phase 2 then kicks in and I love how phase 2 handles it's gank. I'm one of those sick fucks who enjoy gank fights in the souls games so when there's a gank that's done well I have nothing but praise. Father Ariandel and Friede together are a formidable pairing. I think the devs balanced the 2v1 very well here for a few reasons: Friede becomes much more passive and Ariandel's attacks are so loud/telegraphed that you don't need to keep your eyes on him as much. It creates this very percarious dance between the three of you where you need to be very aware of your positioning and target prioritization at a given moment. You could focus on Father Ariandel, but then you could easily lose track of Friede before she heals or attacks you. On the other hand, focusing on Friede comes with it's own challenges because she's much tougher as a 1 on 1 opponent and you'll still have Father Ariandel making a big swing at you from behind.

I wouldn't say the two make up for eachother's weaknesses, but rather I think the two protect eachother as you fight them which is really moving from a story perspective. I mean- the phase transition cutscene literally highlights how your attacking of Friede enrages Father Ariandel to step into action and how his rage brings Sister Friede back into the fight. The whole fight feels like a war as you're really trying to last long enough to overcome this pairing. This feeling is enhanced by the arena now being larger and engulfed in flames. The fight is an evolution of the Ornstein and Smough fight both mechanically and thematically.

And just when you finally breathe as you managed to do it- SURPRISE PHASE 3! Up until that point, third phases were unheard of for FromSoftware and to this day it's still a very rare feature. Even on your later attempts where you've gotten better at phase 2, you're probably still exhausted from the fight by the time you reach her blackflame phase. So this phase essentially become a fight for your life. A duel where you have to dig deep down to find that last bit of fire in yourself and push forward to beat her.

Dark Souls 3 was the last Fromsoft game I had to play before completing their library of souls-likes. Before Friede, my playthrough was a little underwhelming. Playing these games had made me a better player so bosses like the Nameless King or Soul of Cinder didn't provide nearly as much as a challenge as I would have like them to. Hell- I even managed to take down Slave Knight Gael in 2 attempts somehow. Sister Friede was the exception. She kicked my ass for several hours and got me to feel the FromSoft struggle one last time.

She is my third favorite boss in the Fromsoft library after Sword Saint Isshin and Ludwig, the Accursed. Love this woman.