Dream of Dreams
The Dream of Dreams, often shortened to simply the Dream, is a mindscape made up of aether and powerful magic that makes up the sylvari unconsciousness of memories, hopes, and fears and more. A darker side of the Dream, known as the Nightmare, exists.
Many non-sylvari believe the Dream of Dreams is some form of hive mind, but it is not. Before a sylvari are awakened to the world, they experience visions of life within the Dream of Dreams, witnessing various memories of other sylvari and becoming acquainted with the world through these past experiences of other sylvari. The Dream is described as being like a well in these instances, with the memories and thoughts of sylvari being the water. Newborn sylvari are not born with the knowledge of the whole well, but like that of a bowl filling with well water – each developing sylvari only takes a small measure of the information and memories. The Pale Tree herself ensures that each sylvari is then equipped with essential information, such as how to read, basic living skills, the tenets of the Tablet, and the assurance that she loves each of them.
The exact origin and nature of the Dream and the Nightmare remains unknown, but they are sometimes talked about as if they are their own entities, and both seem to actively oppose the six Elder Dragons through the Wyld Hunts and Dark Hunts they send. At least three powerful entities are tied to the Dream of Dreams and have a degree of control over it: the Pale Tree, the White Stag, and the Elder Jungle Dragon Mordremoth. Through these beings, other individuals - such as the sylvari - are able to be connected to the Dream of Dreams, allowing their minds to enter the mindscape and leaving their bodies behind temporarily.
Not all sylvari are connected to the Dream. Malyck, a sylvari born from another tree, did not experience the Dream or Nightmare. It is unclear how many - if any - of the Mordrem are connected to the Dream of Dreams through Mordremoth.
Memories of the sylvari
Because the memories and information received differs among the sylvari, they are not without individualism. Upon leaving the golden fruit from which they are born, they are left to interpret what they saw in the Dream. As such, some sylvari take on the role of mentors to help newborn sylvari understand what they may have seen in the Dream. This includes lessons to explain the Tablet's writings as the sylvari interpret them, a better sense of sylvari history, and education about the world around them. 
The Dream can impart knowledge and sensation, but not actual experience. For example, upon being served a leg of roast moa bird, Killeen told Dougal Keane that she knows from the Dream what it is and how it will taste, despite never yet having tried it herself. Sylvari also have varying degrees of an empathic sense of other sylvari through the Dream, some being so powerful they must distance themselves from others to cope with the sensations, but only the Pale Tree can find true knowledge of memories of recent events in the Dream. Some sylvari, unable to cope with the overwhelming amount of sensations coming from the Dream, intentionally cut themselves off through meditation and become Soundless. Soundless, however, are never completely cut off from the Dream or, in turn, from those who have a degree of control over the Dream like the Pale Tree and Mordremoth. If the Pale Tree needed to speak to a Soundless, she could, but it would need more effort than with non-Soundless. 
The Dream of Dreams is also capable of showing individuals the present and future as well as the past of the world, though the future it shows may not come to pass. Among these visions of the future are Wyld Hunts, compulsions that drive sylvari towards a certain goal. Such compulsions are described as an itching on the back of one's neck, or a tightness in one's chest and a buzz in the back of one's head and will persist until the sylvari completes the Wyld Hunt. Wyld Hunts are seen as a sign of honor among sylvari, and those who receive such are called Valiants. Many Wyld Hunts appear to focus on fighting the Elder Dragons and their minions, even Mordremoth.
The Nightmare is the darker side of the Dream, where painful memories gather most. It was first experienced by Faolain and Caithe on their travels through Central Tyria. Ever since that moment, Faolain was unconditionally changed, from once being the brightest of the Firstborn, to becoming cruel and obsessive. Faolain was not immediately evil, however, as she had not fully succumbed to the Nightmare, and the Nightmare Court, until later, when Cadeyrn who had established the Nightmare Court brought her fully in. The Nightmare Court is a group of sylvari who have dedicated themselves to spreading the Nightmare, believing that doing so will free the sylvari race from the "shackles" of the Ventari Tablet and its tenets. The Nightmare Court preach that the tenets of Ventari's Tablet have affected the sylvari's development, and seek to destroy the Tablet and convert the denizens of the Grove to the "true nature" of the sylvari, within the nightmare.
Like Faolain, all who succumb to the Nightmare become warped and twisted, their new selves craving the harm and death of others, though they still retain part of their original personality and individual. Though it is uncommon, some individuals like Gavin, may retain honor and act without malice. How a sylvari may fall into Nightmare differs, but it is always a traumatic experience; the Nightmare Court attempts to recruit sylvari from various villages outside of the Grove. Those they recruit are then beaten and forced to torture those they kidnap and imprison. There is no "cure" for those who succumb to the Nightmare, however, it is possible for a sylvari who fell to Nightmare to close themselves off to it like a sylvari can close themselves from the Dream, becoming akin to the Soundless. Similar to the Dream's Wyld Hunts, the Nightmare gives Dark Hunts to sylvari, missions that focus around spreading the Nightmare to other sylvari.
In 1328 AE, nearly a year after Mordremoth awoke, he utilized his connection to the Dream of Dreams to send out his Call to all sylvari, using the same channels the Dream and Nightmare use to send Wyld Hunts and Dark Hunts. The Call consisted of whispers in the minds of sylvari, both as its own voice and as a voice that they cannot distinguish from their own thoughts.
- ^ a b Hearts and Minds
- <Character name>: Then we destroy the root: Mordremoth's mind. Its strongest attacks come from its mind, from the Dream. That's our target.
- Canach: Sound strategy, Commander. Turn the tables and attack the dragon the same way it's been attacking us? Brilliant.
- Rytlock Brimstone: (growl) I've seen enough metaphysical landscapes lately. I'll stay behind to keep the Mordrem at bay.
- ^ a b A Light in the Darkness
- Avatar of the Pale Tree: The portal before you is a passage into the Dream. There, you will see glimpses of the past, the present, and the future.
- <Character name>: What is the Dream? I don't understand.
- Avatar of the Pale Tree: The Dream is the sylvari unconscious, the wellspring from which we flow. It holds our memories, as well as our hopes and fears. I am its keeper.
- <Character name: What do you mean?
- Trahearne: The Dream is not reality, <Character name>. It is made of memory, aether, and powerful magic. Even I do not understand it.
- Avatar of the Tree: But be warned—the future can change in the blink of an eye...
- ^ a b Ghosts of Ascalon, page 120
- "It isn't mind-reading," said Killeen, "and we aren't all connected to one big mass mind. However, before we come into the world, the sylvari are united in the Dream of Dreams."
- "We were not there when all this happened, but we know it because of the Dream of Dreams. While we were quickening within the golden fruit of the Pale Tree, the tree spoke to us of the world outside. She taught us, if you will, of the nature of the waking world.
- "We are not all-knowing," she continued. "The Dream of Dreams is not like a tome of all knowledge. But it does give us a life before our life, in which we learn much of the world we are coming into. Fire is hot. Wild animals can be dangerous, but many can be tamed. Her is a proper way to use a sword. This is how you cast a spell, if you are so disposed. We come into the world with knowledge of the world, but not necessarily the experience."
- Riona shook her head. "Is there a difference? Experience gives you knowledge."
- "For humans, most likely," said Killeen, "but not for us." She picked up an oversized drumstick. "This is a leg of a young moa. I know that it was a moa from the Dream, and further that it is well cooked but not overcookedx. I know what it tastes like but have never tasted it myself."
- ^ Comment by Ree Soesbee, Stéphane Lo Presti, Guild Wars 2 Guru
- ^ A Different Dream
- Trahearne: My friend Amaranda spends her life meditating on the Dream. She understands its nature more than any other mystic of firstborn.
- <Character name>: If she studies the Dream, why does she live so far from the Grove?
- Trahearne: Because she is so sensitive to it. She can feel every ebb and flow, like the tide feels the moon. Only far from the Tree can she gain perspective.
- ^ a b c d ArenaNet Lore Interview, guildwars2roleplayers.com
- ^ Village of Astorea ambient dialogue
- Sapling (1): What is it like to feel the call?
- Sapling (2): It's difficult to describe. It's a tightness in your chest and a buzz in the back of your head.
- Sapling (2): You can't stop thinking about what must be done. It gnaws at you and climbs your soul like a parasitic vine.
- ^ Twilight Arbor story mode
- Caithe: Faolain is firstborn like me. She's powerful and dangerous, but she wasn't always that way.
- Caithe: When our race was new, we traveled together, her and I. We became close.
- Caithe: We found a great darkness. I pulled back from it. Faolain embraced it.
- Caithe: Faolain. It wounds my heart to see her like this. She was once the brightest among us.
- <Character name>: She was very important to you, wasn't she?
- Caithe: You may see the repellent creature she has become, but I remember what she was at the very beginning. She was the sun to my stars.
- Caithe: Cadeyrn! May the crows feast on his heart!
- <Character name>: Who was Cadeyrn?
- Caithe: Cadeyrn was one of the secondborn. He brought Faolain fully into the Nightmare Court, and she replaced him as their leader.
- ^ The Newly Awakened
- ^ Beneath a Cold Moon
- ^ Twilight Arbor explorable mode
- <Character name>: Tell me more about Leurent.
- Morrigu: He was a good man once. A lover, an adventurer, even a hero. Now he craves only bloodshed and war.
- <Character name>: What happened?
- Morrigu: It was his Wyld Hunt. He was called to save a village from Zhaitan's undead horde. When I heard that the village fell, I mourned Leurent.
- <Character name>: But he didn't die.
- Morrigu: He returned, darker and different. He blamed me for his failure, saying his love for me weakened him. He left, pledging to bend the world to his order by use of force.
- ^ a b Nightmare Recruit
- ^ Points of Interest Episode 18 Summary, guildwars2.com
- ^ The Dead End: A Study in Scarlet
- Scarlet Briar: Ever since I came out of Omadd's machine, you've been taking credit for my ideas. They are mine! Not yours.
- Scarlet Briar: Let me be clear. I'm not doing this for you; I'm doing it for me. Nobody tells me what to do. Not ever.
- Scarlet Briar: It's not true. None of it. I don't have to listen to you. Get out of my head!
- ^ Prisoners of the Dragon
- Occam: Commander? What's going on out there? Some of my former comrades in the Pact don't seem to distinguish between Mordrem and sylvari.
- <Character name>: It's Mordremoth. The dragon's influence turns some sylvari bad.
- Occam: That explains the terrible voice I hear and the strange thoughts I've been having. But I know who I am, and I swear to you—I am not some Mordrem thrall.