Endings (Hollow Knight)

There are three different endings to Hollow Knight, each requiring a different set of circumstances.

Ending 1: The Hollow Knight
Requirements: Upon defeat, the Hollow Knight dies and the player absorbs the infection into itself. The player is then sealed inside the Black Egg and the game ends.
 * Not having acquired Void Heart

Unlocks the "The Hollow Knight" achievement.

Ending 2: Sealed Siblings
Requirements: Near the end of the fight Hornet will swoop in and fracture the Hollow Knight's mask with her needle before restraining it and giving the player an opening.
 * Having acquired Void Heart
 * Defeating The Hollow Knight

Once the player strikes The Hollow Knight enough while it is restrained, it breaks free (knocking Hornet unconscious) and the fight continues. This causes an alternative ending where, in addition to the events of the first ending, Hornet is also sealed inside, her mask appearing on the door (similar to how the Dreamers' masks were before).

Unlocks the "Sealed Siblings" achievement.

Ending 3: Dream No More
Requirements: While Hornet has the Hollow Knight pinned down, if the player uses the Awakened Dream Nail on them, they will be transported inside Hollow Knight's mind and fight The Radiance. At the end of this fight, the Hollow Knight returns at the end as a shade that rips open the Radiance's face, allowing the player to destroy it.
 * Having acquired Void Heart
 * Defeating The Radiance

After the player has defeated The Radiance, the Infection is defeated and the Black Egg remains open. Hornet wakes up to find the player's mask broken in half at the centre of a crater in the room, implying the player has either died or returned to the Void.

Unlocks the "Dream No More" achievement.

Extra Ending: Passing of the Age
After any other ending, if the player has completed Mister Mushroom's quest by talking to him in all areas, a cutscene will play after the main cutscene depicting Mister Mushroom flying off into the sky.

Unlocks the "Passing of the Age" achievement.

Trivia

 * After any ending, loading the save file again will bring the player back to the Bench inside the Temple of the Black Egg, while recording the defeated Bosses in the Hunter's Journal.
 * This means that if the player acquires the Void Heart prior to reaching the end of the game, they will no longer be able to unlock the first ending from that save file.
 * Acquiring the Void Heart also unlocks the "Void" achievement.