Frenzy flame quests

[The Wang]

was wondering if using the frenzied flame to burn the erdtree would affect my ranni questline ending

[Sickerton]

Frenzied Flame is the only path which tries to lock you in, and the only way out of it is a convoluted set of steps that you can mess up and involves going through some of the toughest optional stuff in the game. While it's possible to wrestle yourself out of it, I'd just avoid the chance and pass on Frenzied Flame entirely.

[Carighan]

Yes and no.

Primarily, yes, since both the "normal" and the Ranni ending become entirely unavailable when you finish this questline.

However, there is a way to undo the effect (look up Millicent on the wiki) and that in turn makes it so as if you had never completed the Frenzied Flame. And despite this technically allowing for a situation that would normally be impossible in regards to one important character, the ending(s) are entirely unchanged, which is a shame - I tried that.

[GrandTickler]

its also the only way to keep Melina alive, if u visit three fingers before the burning of the tree