Nightlight, bright light,
Nightlight is an enigmatic immortal boy that was once the Man in the Moon's bodyguard until he helped seal Pitch away the first time. Since his and Pitch's reawakening, he's mostly enjoyed wandering the earth in addition to bringing his own abilities to the fight. He becomes Katherine's closest friend.
Nightlight is a young boy with a friendly face, white hair, and pale green eyes. His attire appears to be armor and he carries a diamond dagger with him all the time.
Being a boy of pure light energy, Nightlight is very bright, easily shining through any darkness you throw at him. He seems to be made of light and mist and it's mentioned to sparkle in sunlight.
Nightlight is a little shy, but extremely friendly. He is very curious and playful, but is also very loyal to his friends.
Nightlight was Man in the Moon's bodyguard when he was a baby. Every night, he would sprinkle Dreamsand on the baby and watch over his dreams for Nightlight never sleeps. Before Man in the Moon's parents were going to face Pitch, they had Nightlight take an oath and protect their son within the Moon Clipper. During the battle, Man in the Moon was so scared, that he cried and Nightlight caught the tear and repeated the oath and the tear hardened into a diamond dagger. After bidding good-bye to his ward and taking the dagger, he entered the battle. At this time, Tsar and Tsarina Lunar were captured and Pitch almost won until Nightlight went and stabbed Pitch in the heart with the diamond dagger and caused an explosion brighter than twenty suns. Pitch fell into a dark cave and Nightlight was trapped in his cold heart. He remained there until a moonbeam accidentally entered the dagger awakened him and unintentionally Pitch as well. When Nightlight was freed, he had no memory of who he was and tied his dagger on stick and created a staff. When he saw the sleeping in a nearby village, an old memory appeared and faded in his mind which left confused. However, he was free and traveled until he saved the children of Santoff Claussen from an fearling attack. From time to time, Nightlight would travel the world and play tag with the moonbeams and also get curious about the people on Earth.
Powers and Abilities
Nightlight was the guardian of the Baby Prince of the Moon. The Nightlight was a special being. The only one there ever was. A boy of light who could live forever and never grow old. And he would always protect the royal young of the Golden Age, especially from nightmares. He would never sleep. And be always watchful. 
Known to be the fastest boy who ever lived. Can take someone with him with relative ease (like when he caught Katherine, falling for 3.5 seconds from the highest tower of the Lunar Lamadary in Toothiana: Queen of the Tooth Fairy Armies).
Although he's the fastest, it's stated that he's far from the strongest: even hundred Nightlights wouldn't be able to keep in the air a marble Nightmare Rock.
Nightlight has the ability of the Magic Kiss of the Good Night. Which is considered so powerful that it takes away all the hurts and makes the scare and sad go away. A drawback of this ability is that Nightlight can never give it and stay a nightlight. 
To known degree Nightlight can use telepathy (same as Sandman or Mother Nature) to communicate: himself and the person he's "talking" to would know each other's thoughts and feelings. If he tries to hide something, person stops feeling him. But if taken by surprise, he might not be able to hide his feelings even if he wants to.
He feels if someone tries to read his mind without his permission.
Nightlight is perfectly able to control how exactly bright he is. From using his glowing as flash in order to interfer his enemies and blind them for a moment, to the point where he can nearly hide in shadows. His brightness varies depending on his mood.
He is known to use light in order to create a road in the air for reindeers to run upon.
If Nightlight gets someone's tears of sorrow, he can turn them into a diamond blade. Or use them to fix the broken one. Originally his blade was created by himself using tears of baby MiM, then the blade got shattered and fixed with tears of children of Santoff Claussen in E. Aster Bunnymund and the Warrior Eggs at the Earth's Core!, and finally Nightlight adds his own tears of sorrow in Toothiana: Queen of the Tooth Fairy Armies.
- "Nightlight, bright light, sweet dreams I bestow. Sleep tight, all night. Forever I will glow."
- "Remember me in dreams."
- "We fear you none!"
- "Will my Katherine go Darkling or stay true?"
- "Only that he's gone to help Katherine. And that none of us should follow."
- "Katherine's story! Her life! Her hurts! HER! That's what we save. Remember your knowing. Be stronger than the scared and the hurt, and dream a way to save our Katherine!"
- "Be writing what just happened on your pages, Mr. Q. That today Nightlight, the boy Guardian, had the knowing of a Tall One."
Before Nightlight was transformed into Jack Frost, he was the most trusted and valiant companion of Mim, the Man in the Moon. His actions have influenced and protected the Guardians in many ways. Nightlight's self sacrifice protected MiM from Pitch long enough for him to become an adult. It also inspired MiM to become the Guardian of the Children of Earth and to call to his side a band of heroes to serve as the Guardians.
Nightlight has also saved Katherine from falling, and saved her from Pitch's nightmares by giving her the Good-Night Kiss. Furthermore, Nightlight has help the Guardians figured out what Sandman's sand was capable of doing and how to unlock its magic.
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related to Nightlight.
- Nightlight rarely talks, but he can convey conversation through gestures and drawings. This behavior is similar to Sandman's.
- The tip of Nightlight's spear contains a moonbeam, the very same one that had accidentally trapped itself inside while also setting Nightlight free from his centuries of entrapment with Pitch.
- While never confirmed, there is an implication in the book that Nightlight possibly has several other powers that are rarely shown such as the ability to shapeshift and go invisible.
- In the first book it's mentioned that Nightlight was able to shapeshift himself smaller in order to be able to fit inside his diamond dagger when it was impaled inside of Pitch's heart, later turning back into a boy after being freed and later it's mentioned that Nightlight turned himself into multiple fractals of light to form a protective shield for the children of Santoff Claussen.
- He's also able to transform tears and is even able to make his dagger bigger by adding tears to it.
- There's also the fact that as Jack Frost, Nightlight can physically manipulate his age.
- The ability to go invisible is implied by the fact that Nightlight spent months watching over Santoff Claussen without being detected, though it's possible that he may have been shapeshifted form during this; and later was able to follow Sandy to find Katherine without being detected.
- He's also mentioned to be able to make others invisible by the fact that he was able to rescue Katherine (who had Nicholas and Ombric's doll forms in her arms) before disappearing into 'lighted mist'.
- Katherine also mentions in the second book that she can't see him when he's hiding in the trees, but senses him instead.
- Nightlight doesn't remember much about being Baby Lunanoff's protector, but can recall the long years trapped inside Pitch's cold heart after sending Pitch down to Earth. He eventually remembers his past after coming in contact with Sandy's Dreamsand in The Sandman and the War of Dreams.
- The character of Jack Frost has a striking resemblance to Nightlight, one fact being they have similar personalities, both of them used a staff as weapon and they both have white hair.
- Jack Frost revealed that Nightlight and Jack were the same person.
- In The Sandman and the War of Dreams, Nightlight gives Katherine a “Kiss of Goodnight” on the lips which awakens her from her spell as well as him become a real adolescent boy who will finally age like everyone else.
- Even though Nightlight strongly prefers to use telepathy, gestures, drawings, etc. in order to communicate, he isn't mute. In The Sandman and the War of Dreams his voice is described as "mesmerizing, otherworldly". Also there's stated that only the direst of circumstances could compel him to use his voice.
- It's implied that Nightlight and Katherine have begun to develop romantic feeling towards one another as The Sandman and the War of Dreams mentions that Katherine and Nightlight share a distinct happiness that only the closest of friendships have after going through a "great change".
- Prior to that in the books mention that Nightlight was drawn to Katherine.
- They have a deeply close bond, one of a connected heart and mind.
- Nightlight refers to Katherine as "My Katherine" when talking to the Man In The Moon.
- It's described that they can understand each other without even needing to talk, “A friend who understands everything without being told is the rarest and best kind of friend”.
- Pitch also tries to threaten Katherine as a way to terrify Nightlight, something Nightlight immediately recognizes.
- Katherine is described as being worried when she can't sense Nightlight, his friendship or anything from him at all.
- Nightlight is afraid of the thought of Katherine growing up and leaving him behind because he is unsure as to if he has the ability to grow up himself.
- There's also the fact that Nightlight willingly gave up being a "Nightlight" by kissing Katherine so she could wake up, resulting in him being able to grow older (And thus growing into Jack Frost).