Hollow Knight features three different endings that can be unlocked during a single playthrough. Each has its own requirements, although once you meet the conditions needed to access the more advanced endings, you will no longer be able to view the earlier ones. We therefore recommend watching them in the order shown below.
This is the most basic and standard ending in the game. All you need to do to see it is defeat the Hollow Knight without acquiring the Void Heart. After watching it, you will unlock "The Hollow Knight" achievement, the ending will be recorded in your journal, and you can continue playing from the save point just before the final battle to unlock the other two.
To obtain this ending, you simply need to acquire the Void Heart and defeat the Hollow Knight. If you do this, Hornet will appear during the final part of the battle and crack the enemy's shell. When this sequence occurs, attack your opponent so that it breaks free, allowing the battle to continue until you finish it off. This unlocks the "Sealed Siblings" achievement.
This is considered the game's true ending. The requirements are similar to those for "Sealed Siblings", except that when Hornet appears and restrains the Hollow Knight, you must strike it with the Dream Nail. Doing so will transport you inside its mind, where you can confront the true final boss of this epic adventure: the Radiance, a formidable opponent who will constantly keep you on the defensive. Defeat it to unlock the "Dream No More" achievement.
There is a short additional scene that can be viewed after any of the three main endings. To unlock it, you simply need to complete every stage of Mister Mushroom's quest, which you can easily do by speaking to him in every area where he appears throughout your journey. Doing so unlocks the "Passing of the Age" achievement.
The Void Heart is an item required to unlock the second and third endings. To obtain it, you must travel to an area called the Birthplace, located at the very bottom of the Abyss, beyond a sealed door.
Naturally, opening this door is no easy task, as you must have the Kingsoul equipped, a charm obtained by collecting its two halves. The first is given to you by the White Lady, who can be found in the northwestern section of the Queen's Gardens, just beyond a battle against a powerful boss.
You will obtain the other half by completing the White Palace, a secret area accessed by striking the Kingsmould's corpse in the southeastern corner of the Ancient Basin with the Awoken Dream Nail. You will need to collect 1,800 Essence before the Seer will awaken it for you. This area is a pure platforming challenge, and the other half you need can be found at the very end.
Once you have completed the Kingsoul and passed through the door in the Abyss, you will reach an egg-like object. Strike it with the Dream Nail to trigger a cutscene and finally obtain the coveted Void Heart.
