Radiance

"The light, forgotten. The plague, the infection, the madness that haunts the corpses of Hallownest... the light that screams out from the eyes of this dead Kingdom. What is the source? I suppose mere mortals like myself will never understand."

The Radiance is the secret final boss of Hollow Knight. Absolute Radiance is her perfect form.

Lore
The Radiance is a higher being of light similar to Essence, and as such, opposed to the Void, her ancient enemy. The Moth Tribe is born from her light and in return revered her.

In-game events
From her prison, the Radiance, heart of the Infection, plagues the dreams of bugs. She infects Myla, causing her to attack the Knight, and uses Lightseeds and Infected flies to reanimate the Broken Vessel and the Watcher Knights. After killing at least one Dreamer, or obtaining the Monarch Wings, the Infection worsens in the Forgotten Crossroads, turning it into the Infected Crossroads, and making its bugs more violent and dangerous.

Her fate is linked to the end of the Knight's journey. By defeating the Hollow Knight, the Knight is able to seal the Radiance within, taking the place of their sibling within the Black Egg.

Behaviour and Tactics
Attacks

Phase Breakdown

Charm Sets

To access the Radiance, the Knight must have acquired Void Heart and have used the Dream Nail on the Hollow Knight when Hornet holds them down. The Radiance does not count as a regular dream battle, so the Hollow Knight needs to be fought from the beginning on every death.

In the first Phase of the fight, she levitates slightly above the floor. Only her body is vulnerable to attack, which requires jumping or ranged attacks. She often teleports around, making it even harder to get a good string of hits while avoiding her own ruthless attacks.

The Radiance does not deal contact damage; however, all of her attacks except summoning spikes deal two Masks of damage. Falling off the platform only deals one Mask of damage.

The Radiance has a wide variety of attacks, each with a variety of mitigations.
 * Beam Burst: A beam never strikes in the same place consecutively (so burst 1 and 3 may be almost exact). The Radiance does not move during this attack, and therefore spells like Howling Wraiths/Abyss Shriek or Nail Arts are a viable option, given her large hitbox. Healing without Charms can be done throughout this attack (especially with lucky burst patterns) but healing is safest to start once the third burst pattern is known.
 * Sword Burst: Everything said about the Beam Burst applies to the Sword Burst except in this case, there is only the one burst to consider. Thus, the Knight can begin healing just about as soon as the attack starts.
 * Sword Rain: The Radiance teleports during this attack so damaging her while dodging the swords is difficult. Abyss Shriek is useful at the end of this attack, and Nail attacks allow for flexible and quick damage while the Radiance is within reach. Healing without Charms is possible once the last set of swords is seen or throughout the attack if arrangement of swords allows for it.
 * Sword Wall: The Radiance teleports during this attack, so damaging her while dodging the swords can be difficult. The safest method is to use Nail attacks when the Knight is near the Radiance. It is possible to use the Shade Cloak and dash through the swords, but it is not possible to dash through all of them, since the Shade Cloak has a cooldown. Healing without Charms is only viable if the wall patterns are forgiving or the Knight starts healing on the side of the arena opposite the wall's spawn. This is more forgiving in Phase 4 because the walls move slower.
 * Wall of Light: This attack must be dodged either with a shadow dash or Descending Dark. The Radiance teleports during this attack so quick damage is most viable. Healing without Charms is safest if the Knight gets through the wall quickly or starts healing when a wall spawns on the opposite side of the arena. This is more forgiving in Phase 4 because the wall moves slower.
 * Orb: The Orb attack requires quick movements. It is best to try to bait Orbs into the floor or platforms to destroy them early, leaving more time to attack the Radiance. Using the Shade Cloak to dash through a projectile destroys it, and can be useful if multiple projectiles are close to each other. There is no time to heal without Charms or getting lucky with the platforms in Phase 4.
 * Spike Floor: The Radiance spawns short spikes covering half of the floor. Unlike all other attacks used by the Radiance, this attack deals only one mask of damage. The spikes disappear for up to 5 seconds if struck by the Knight's body or hit with Descending Dark. The spikes almost immediately return in Phase 3.
 * Beam: The Radiance fires one beam of light, targeted at the Knight. This attack becomes more accurate the higher the Knight gets during Phase 5. It can be baited to fire and miss the Knight, since the attack is used at regular intervals.

Location
The Radiance's fight can be accessed by using the Dream Nail on the Hollow Knight in the Temple of the Black Egg.

Trivia

 * There is a statue of the Radiance at the top of the map in Hallownest's Crown where a Pale Ore can be found. Dream Nailing this statue yields the lines:
 * "...Remember... Light..."
 * Through HUD manipulation, the Radiance is shown to actually have 3000 health, though the "fight" portion of the battle ends when she reaches 1300 health, effectively requiring the Knight to only have to deal 1700 damage to win the fight.
 * The Radiance is one of the two bosses that has a full-screen title card, the other being Nightmare King Grimm.
 * The Radiance must be challenged to a battle the first time she is fought after loading a save file. Her introduction is abridged after dying to her once, causing her to attack directly upon entering her arena. The introduction returns after reloading the save file.

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