Beat the Hollow Knight to get this ending. Hornet will eventually pass out and the fight continues.

When Hornet interrupts, don't strike the Hollow Knight with your Dream Nail, but continue your attacks. To get this ending, obtain the Void Heart and enter the Black Egg.

Sealed Siblings - A semi-hidden bad ending.

In this ending, you kill the Radiance and end the cycle. After you complete it, you can watch the ending. Hit the Hollow Knight with the Dream Nail. Halfway through the fight, Hornet will interrupt by hitting the Hollow Knight with her nail and tying him down. Enter the Egg and fight The Hollow Knight. This will change the Kingsoul into the Void Heart. At the bottom of the Abyss, strike the mirror with your Dream Nail and ascend from the Abyss in the Dream World. Descend down the area, killing or dodging the Siblings. Go to the bottom most section of the Abyss and enter the newly opened cave area. This will make you leave the Dream World and will kill the Knight. After striking the King's corpse, you must pick up the other half of the Kingsoul. Optionally, you can go to the right of the king and read his last message or sit on the throne. At the end of the palace, strike the king until his corpse drops from the throne. This will transport you to the Dream World, where you must complete the difficult White Palace. After awakening the Dream Nail and obtaining the first half of the Kingsoul, strike the Knight sitting outside the Palace Grounds. Additionally, go to the Queen's Garden and obtain the White Crest Fragment.

You need a total of 1800 essence to fully awaken the Dream Nail (2400 essence is required to hear the Seers last words, but this is optional for this ending). Additional essence can be gained from the various non hostile spirits and the Dream Trees scattered around the map. To get this ending, first obtain a fully awakened Dream Nail by killing the various spirit bosses, the Champion versions of False Knight (Failed Champion), Soul Master (Soul Tyrant) and Broken Vessel (Lost Kin). This ending becomes locked after obtaining the Void Heart. In this ending you take the place of the Hollow Knight, continuing the cycle. To get this ending, kill the Dreamers and enter the Black Egg straight away.

The Hollow Knight - The default ending.

The endings are in order of obtainability (named after their associated achievements): Currently (version 1.0.1.4) there are three endings and one post-credits scene that can be unlocked.

How to upgrade nail hollow knight