In stories, the third time really does usually succeed when the first few times fail for unexpected reasons. The narrator's request makes narrative sense! So, you decide to slay the princess.

You make your way to the cabin in the woods. You go inside. There isn't a table at all, or a dagger. There is a mirror, but you smash it, bloodying your fist.

"We're not going to take it any more!" the voice of vengeance screams.

"Don't do this!" the voice of the boss says. "You're supposed to listen to me."

"I just want to knock everything down!" you say. "I'm tired of this obnoxious storybook I seem to be trapped in."

"You're going with 'trapped in a storybook'... fair enough," the narrator says. "Yeah, that's what this is. Kill the princess and get out of the story book. Then, marry your groom. The Princess' Groom--a good title for a Neverending Story. Still better, the princess is a pony--ponies have grooms, but you aren't supposed to marry her... that doesn't work. Besides, it already happened. Perhaps instead, we need a Labyryinth."

"What nonsense are you sprouting?" you ask.

"References from a universe's 1980s movies. I play them for myself while I'm waiting for you to do something."

"Don't listen to the narrator! Smash everything and then kill the narrator!" the voice of vengeance says.

"That's why you're on board with killing the princess? Order of operations doesn't matter?" the voice of the boss asks.

"Yeah!" the voice of vengeance calls out.

You try to open the door to the basement. It's locked. You knock it down with a heavy shoulder. It snaps and you head down an Escheresque staircase. Then you head up. You head right. Left. Up. Down. It takes an eternity. You reach the ground. The walls close in--they shift and they turn.

"We should track where we go in this... labyrinth... with something, a string, perhaps."

"We don't have a string," you say. Then, you prick your body with a claw. Blood drips. "We'll use this."

"A blood trail... at least it can't be cut," the voice of the boss says. "I admire your inventiveness, at least."

"Blood!" the voice of vengeance says with delight.

You trace your trail and, able to avoid going over the same place twice and to foil the shifting walls by smashing through a few of them, you meet the princess. She's chained by iron, has the head of a minotaur, and clenches her teeth--set and seething with an indomitable will.

"Iron Will?" you ask, momentarily confused. "I mean... you will not dissuade me from my task. I have an iron will. I think that's what I meant to say."

"Iron will meant that much to you?" the narrator asks. "Actually... ignore that."

"That phrase reminds me of a name..." the voice of the boss says.

"I will grind your bones to make my bread," the princess threatens and pulls at her chains--they strain against the wall and then you hear the shuddering. The stairs collapse. The walls collapse. The princess has brought down the structure. You are struck by a stone.

And then you die.

*.*

Author's Note

This is an "Act Three" ending.

This "Act Three" is structured different from how the game did it, to encourage you to purchase the game if you liked this adventure.

Consider this Act Three ending a 06: Disaster ending.
It's also the Joker ending, featuring Iron Will.

There isn't a lot of insight with this ending,
although there is some metatextuality.
You indeed are trapped within a storybook.
And the logic of "three tries" should have worked.
You'll have to break its rules to see the larger picture.

You can start again and try to find a different ending or to track down the memories of Applejack, Fluttershy, Rainbow Dash, Rarity, and Pinkie Pie.