Knock Knock has two endings, which are precursored by a note you receive near the end of the game: it reads Don't look in the mirror, look out the window. This isn't a part of the protagonist's diary (which was collected earlier on in the game): it's from the invisible child which has been hinted at several times with notes (and encountered if the player searches the forest during the reality stages, and the house during the dream stages).
There's also a failure state which could be considered as an ending, but it gives you the option to replay the level should this ending appear. This state involves either staying out too long in the woods, or getting caught by the Guests too many times within the dream stages. It involves the protagonist going mad (in the forest, it's precursored by him acknowledging his insanity).
Breaking the CircleEdit
To achieve this ending, players must find at least 6 pieces of reality. In this ending, the protagonist follows the instructions of the note, boarding up the windows of the house and (it's implied) leaving the building. There's the invisible child, who watches it become overgrown with plants.
At this point it's seen whether the player got the best ending or simply the good ending: In the best ending, the house is overgrown with green plantlife that looks alive; while the good ending has the house get overgrown with thorns and vines. The best ending is triggered when the player has found every possible encounter with Dashenka: if the player misses even one, it shows the good ending. These endings signify the Protagonist breaking the repetition of levels in the game.
A little bit of help to the people who want to get this ending. In the woods you can find the little girl by the sound of birds singing (not to be confused with crows). If you hear this singing then you should look nearby carefully. The girl is definitely very close to you.
The indicator of that player is going to get this ending is The Main Guest being the giant girl.
Player gets this ending if s/he doesn't manage to find at least 6 pieces of reality. In this ending, the protagonist looks into a mirror (contradictory to the note) and proceeds to board up his windows and it's implied that he seals himself inside.
The indicator of that player is going to get this ending is The Main Guest being the giant monster.
- One of the creators of the game mentioned that 'Knock Knock' has neither good or bad endings. 'Game Over' doesn't count as a full ending at all.