Hell's Narrator

I personally believe the the narration is only directed at the player and cannot be heard by Quote or any other character in the game.

I always thought it was something someone told Quote years ago on the island, and that it starts coming back to him at various times, such as when he's unconscious in the Core room, and in the Sacred Grounds, perhaps brought on by the presence of Ballos.

This is made obvious by the fact that neither Quote nor Curly knew anything about Misery's curse until after Balrog mentioned it despite the fact that the narrator spilled the beans well before then.

You don't know that Quote didn't know. For all we know, he could have just not told anyone. It is true that, contrary to what some have been led to believe, Quote speaks on several occasions in Cave Story, but the credit art images depicting Quote's expression do imply a somewhat introverted nature. I've inferred from that, along with the fact that the Egg Corridor Cthulhu in Curly Story refers to Quote as Curly's "quiet friend," that Quote is a robot of few words. Therefore, he could have simply not told anyone. Additionally, since they were fighting for their lives, Quote wouldn't have been telling Curly any of this during their battle in the Sacred Grounds or with Ballos, and when the walls were closing in, they were worried about their lives. The only time where it would have been fit to tell Curly what he knew about Ballos would have been after Balrog saved them. But before he got a chance to do that, Curly and Balrog conversed. And before Quote got a chance to say anything, Balrog told them some of the things you were told by the mysterious voice. After which, Quote could think that all the additional details were trivial.

 

I always thought it was something someone told Quote years ago on the island, and that it starts coming back to him at various times, such as when he's unconscious in the Core room, and in the Sacred Grounds, perhaps brought on by the presence of Ballos.

The only ones who knew anything about Ballos (himself aside) was Jenka and Misery, oh and Ballos' ghost dog. Jenka had never met Quote before the events of CS. Plus the speaker talks about Jenka, Misery, and Ballos in third person, so by extension it can't be any of them. So it cannot be a memory.

You could counter-argue that the spirits of the dead or some such are relaying this, or anything outside of Quote's memory, but that would mean that Curly would hear it, because she is very much lucid during the part about Misery.

The way I see it the narrator is Pixel and it's only recipient is the player.

All I know is no mention of Ballos is made throughout the game, but suddenly Curly somehow manages her way to Hell at the end? Even though she is still damaged?

Hell is directly connected to the Plantation. Curly was probably heading for the Balcony to find Quote. She could not use Momorin's rocket as she had no association with her and didn't know the password so she needed an alternate route. To put it simply I believe she traversed Hell in reverse and hit a dead end.

 

The only ones who knew anything about Ballos (himself aside) was Jenka and Misery, oh and Ballos' ghost dog.

That, and possibly the Cthulhu. They're all over the island, and the credits describe them as "native inhabitants," so they've been there for a long time, and could very well know about ancient historical events that took place on the island, and therefore know about Jenka and Ballos' history. That would also explain why

the speaker talks about Jenka, Misery, and Ballos in third person, so by extension it can't be any of them.

Jenka had never met Quote before the events of CS.

True, but it's possible that Quote heard about her before his amnesia, or that said Cthulhu assumed he knew due to it being common knowledge among his own kind.