Well, in the interest of completion (I almost spelled that "compleation" as I've been running a D&D game set in Ravnica with the Phyrexians as the big bads) I beat Elden Ring (for the 5th time,) finally picking the Lord of Frenzied Flame ending (I've done Age of Stars three times and Age of Order once - I'd intended my previous character to go Duskborn but then the transfer from my PS4 to my PS5 lost my trophies, so I wanted to have Age of Stars first).
Anyway, I'm feeling a little bummed because I generally err on the side of "good" endings (admittedly what constitutes a "good" ending in FromSoft games is always up to interpretation. Personally I think the most likely ones to count as good are Order and Duskborn) but this is almost certainly the worst. Like, the Age of Curses or whatever the Dung Eater one is surely seems pretty bad, but I'm not convinced that the Seedbed Curse is actually necessarily evil so much as the return of kind of wild, primeval magic of the Crucible.
But the Frenzied Flame has got to be bad, right? Given Melina survives (also: I think at this point we can be pretty certain she is the Gloam-Eyed Queen, right?) I think it's really just the Erdtree and Leyndell that are melted into Frenzied slag (the presence of large burning fingerprints on the walls is perhaps a worrying sign that the Three Fingers are still around) though the world is surely going to have a lot more frenzied folk going around.
One thing that is very open to interpretation is just what the Frenzied Flame is and where it came from. There's a possibility it's one of the Outer Gods like the Formless Mother or the unnamed Rot God. Some put the Greater Will in that category. Personally, I believe that the Flame is something like a corruption or perversion of some other principle - possibly the Greater Will. If you think about it, the Golden Order holds the Law of Regression as one of its key premises. The Frenzied Flame promises to burn and melt everything down back into a single whole.
I think it's implied that the Three Fingers and the Two Fingers were probably once part of a unified entity (there was even another ending, I believe, that never made it live, which would have seen the two united in the Age Absolute). I also think it's notable that melting things together is exactly what one does in a crucible, and thus the Crucible, which was a previous form of the Erdtree, might have represented a healthier version of this reunification (in that case, we have things like the so-called Misbegotten who were originally viewed as blessed because they mixed human and animal traits).
Something's deeply wrong with the Frenzied Flame, though, and it seems to be one of the more Cosmic Horror-like things in the game. There's another questline that never made it into the game involving the Wandering Merchants, where it looks like they were accused of being Frenzied Flame worshippers and were the victims of a pogrom, leading some of them to then turn to the Flame out of a despairing desire for vengeance. (If you've gotten the Frenzied Flame ending or just been to the Frenzied Flame Proscription, you've seen the massive number of bodies of these people sealed up beneath the capital.
Indeed, the Flame is kind of seductive. Vyke, whom we fight once as an invader in Liurnia (and need to fight to do Hyetta's quest) and later in an Evergaol, looks like he was basically going on the same journey as we were, and got farther than any other tarnished, but when he realized he'd need to burn his Finger Maiden to reach Marika, pursued the Frenzied Flame as an alternative. Indeed, we can do the very same to avoid killing Melina, though she begs us not to risk it. The difference, though, is that if we also do Milicent's quest line and purify the Unalloyed Gold Needle after defeating Malenia, and then doing some crazy time shenanigans by traveling to the distant... um, past? Or Future? where Placidusax is, we can cleanse the Flame and thus both spare Melina and avoid allowing the Frenzied Flame to consume the world. (Once again, the fact that Miquella seems to have found a way to save people from Outer God influence - presumably intending first to save his sister from the Scarlet Rot, but happily also saving us from the Frenzied Flame - reinforces my impression that he might be the most good-aligned character in the lore - though watch the DLC show that he's actually some horrifying monster).
One of the creepiest things about the Frenzied Flame is its association with body-snatching. We meet Yura early on in Limgrave, a badass samurai who hunts Bloody Fingers (basically, people who go around murdering other Tarnished). However, when he dies, we see his body again possessed by a figure named Shabriri (a figure/curse from Jewish folklore associated with blindness). Shabriri is referred to as a demon, and seems to very much be one (fun fact, you can summon him to fight Godfrey at the end of the game, and he'll fight alongside Nepheli Loux, who must not know who he is - oddly you can even do this after you get Yura's old gear, though he still seems to be wearing it). Hyetta's an odder situation, though. Like Shabriri, she seems to be possessing a corpse - in this case, Irina, who asks you to take a letter to her father, Edgar, in Castle Morne. Upon beating that "medium dungeon," Edgar finds his daughter killed by Misbegotten, but you then see Hyetta in Liurnia shortly after beating Godrick the Grafted.
Unlike Shabriri, however, who seems to fully understand the Frenzied Flame and all the chaos it would entail, Hyetta seems to be an innocent. Frenzied Flame cultists come and bring her "Shabriri Grapes" to eat, and after you give her a few, and tell her what they are (Frenzied Flame-melted eyeballs, for the record) she is horrified and throws up - though she gets over this because of the effect it has on her kind of inner-vision.
Ultimately, Hyetta winds up fully committed to the Frenzied Flame, and basically becomes the Finger Reader for the Three Fingers, giving you their message and the Frenzied Flame Seal as the Frenzied Flame melts her own eyes and then, it appears, her entire body.
So, is Hyetta a demon like Shabriri? It seems odd if that's the case that she wouldn't be fully on board from the get-go.
Anyway, even if we purge the Frenzied Flame from ourselves, Melina doesn't come and congratulate us. At the very least, we can feel confident that she survives if we don't burn her at the Forge of the Giants.
That said: are we sure she dies if we do?
Melina is insistent that you don't pursue this path. She is committed to her role as "kindling maiden" to burn the Erdtree. And there are several hints, in fact, that she's a secret daughter of Marika, not the least of which is that of the three Butterfly crafting items we find, we see plenty of Smoldering Butterflies along with the Nascent and Aonian ones. The latter two can easily be affiliated with Miquella and Malenia, respectively, and Melina's appearance and name are both consistent with the possibility that she is another child of Marika and Radagon (which is to say, of Marika). Early on when we meet her, she talks about being burned and bodiless - and indeed, she already has burn marks on her hands.
Is it possible that this isn't the first time she's burned the Erdtree?
If we take into account the story of the Wandering Merchants, which is, yes, technically not canon as it got cut from the game, we get an example where a state of ironic cruelty led to people embracing the Frenzied Flame. Likewise, if we look at Vyke's story, it appears he took on the flame in the hopes of saving his Maiden, but we can find her dead body in Liurnia, possibly killed by a Bloody Finger.
Maybe the Frenzied Flame's whole deal is promising a way to save someone we love or avenge ourselves, but only when the damage is already done?
If you get the Frenzied Flame ending, and you get the flame before you burn Melina at the Forge of the Giants (luckily, you can't purge yourself of the flame before you get to Farum Azula, so you'll never be in a state where there's no way to light the Forge) Melina will seem to vow to kill you, revealing herself (I'm about 99% certain) to be the Gloam-Eyed Queen, who, you know, was the original holder of Destined Death.
So whatever good intention you might have for taking on the flame, Melina's not going to be happy you did. Sure, that could be just because she was willing to sacrifice herself to save the world, but it'd be all the richer if she was willing to do it because it was actually no price at all.
Anyway, I don't know if we're likely to get more about the Frenzied Flame in the DLC or even future games (of all the Souls-like games, this one is the one I can most imagine them doing direct sequels to like Dark Souls).