LORE and INFO: The Nightmare appears at the very bottom of the Transmission of Pale City to rip it apart after it is summoned. Six and Mono are supposed to use their powers at once for the true final boss to appear. In order for Six to still be at your side, the player has no choice but to pull her down into the bottom of the tower WITH them in order to fall into the Flesh Basement (with the chair) and use Six's instakill ability and Mono's matter ripping ability at once on the flesh around them. After one wall is destroyed, The Nightmare will soon appear to unlock the true ending after you fight it, with the city constantly being eroded and the walls of the Transmission broken. The goal of the fight is to stop The Nightmare from destroying the Little Nightmares world, and the backgrounds and settings flash to different places, some even referencing the previous game and bosses of both games. After you destroy The Nightmare, you will unlock the true ending (the good ending), where Six and Mono grow up together as best friends, forever improving the Pale City and living in it. There are now no more nightmares. And they lived happily ever- The screen cuts to red. Just red. Then, black text fades in, asking one question- What will become of our heroes? The Thin Man and the Lady are watching. They will destroy the Big Dreams world and turn it into a dystopian wasteland. This is the reason why Little Nightmares 3 looks like the world has been ruined. It was because of them. It was all their fault. [Not the Thin Man.] [Not the Lady.] [Not even The Nightmare itself.] [But THEM.] An image of Mono and Six appears traced in black. The red screen becomes black and all is silent. Everybody's talking about what's in the nightmare. But nobody's talking about the nightmare itself. You have unlocked the END ending.
Song used: Alone Forever (Instrumental) I give credit to @249522 for the original and @CAYDENKINGTREX for the template.