Hollow Knight

Behaviour
The Hollow Knight is the Vessel that sealed away the Infection. It is one of two final bosses of the game.

Upon breaking the seals on the temple by destroying the three Dreamers, the player is allowed entrance in order to fight this boss. To begin the fight, the player must break the four chains holding the Hollow Knight.

Trivia

 * It is unknown as to why the Hollow Knight begins to stab themselves halfway through the fight. It could be trying to help the player by attempting to kill themselves, or they could be trying to further increase their strength by opening up the Infection more, in an act of desparation. It could also be going mad and trying to destroy the Infection that's slowly taking it over.
 * It is explained through NPC dialogue that the Hollow Knight could not contain the Infection due to an unnoticed flaw which caused the them to not be "completely hollow."
 * It is implied that, in the first ending ("The Hollow Knight"), this will also happen to the player - they also failed to become completely hollow, and eventually the Infection will leak through once again.
 * In the Sealed Siblings ending, the player is noted by the White Lady to have become truly hollow due to acquiring the Void Heart, and thus able to fully contain the Infection. Whether this is actually true or another assumption that could be proven wrong remains unknown.
 * During the scene in The Abyss, before the player receives the Void Heart, a Vessel similar looking to The Knight is shown exiting the Abyss with the The Pale King. Judging by the shape of its horns, it seems that it's the same Hollow Knight fought in the Black Egg Temple. It also looks at The Knight before following the Pale King out. This also could hint towards the original not being completely hollow, as it displayed some form of sympathy or sadness.
 * It is unknown if the Hollow Knight has a second arm, as they performs most of their actions with just one arm, and never show a second arm during the battle. Their Shade, however, appears to have both arms.
 * During the ending sequence of The Radiance fight, the Hollow Knight's shade appears and opens up a weak point on The Radiance's head, allowing the player to land the finishing blows.
 * The Hollow Knight has cut Dream Nail dialogue which are the following:
 * ...Kill...
 * ...Shall blaze free...
 * ...This Vessel, broken...fails...
 * ...Dawn...Shall break...
 * ...No mind, the usurper...Only strength...
 * ...Kill the usurper...Our light it would suffocate...
 * ...Father?...

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