Hello Darkness my old Friend: Lucid Nightmare

The Lucid Nightmare is one of the complex Secrets of World of Warcraft. The Mount got added in Legion and to obtain if you will need to solve a series of Puzzles.

This could take a while, so bring a hot beverage and move your character to Dalaran!

Secrets of Ulduar
You will find the first note on a table at the top level of Curiosities & Moore in Dalaran.

It begins in the 2104059.
With a most pleasing sign.
(These letters will not always rhyme.)

Fly over to Ulduar and find the rusty lever in the North-West corner of the Scrapyard.
Click the lever and a 20 by 20 grid of Scrapyard Lights will appear on the floor of the room. Click the lights to form the pattern below and then the Inconspicuous Note will appear:

The Mind-Seekers seem to have a penchant for leaving their notes in obvious places. Maybe they want us to find their treasures? Maybe they feed on our thoughts? That's probably not important…
What was important was an Inconspicuous Note, sitting on a table in the Curiosities & Moore shop in Dalaran (Broken Isles):

It begins in the 2104059.
With a most pleasing sign.
(These letters will not always rhyme.)

2104059, of course, is an anagram of 2009-04-15, the date of the Ulduar patch notes on the official World of Warcraft site. From there, players combed Ulduar for clues. Observant players discovered a new lever in the XT-002's room that they could interact with among the piles of scrap. Pulling this lever summons a massive 20x20 grid of Scrapyard Lights on the floor of the room. Interacting with these lights toggles them on and off.

In the Inconspicuous Note, the Mind-Seekers requested a "most pleasing sign." Many signs and symbols appear in Ulduar, the most prominent being the four symbols of the keepers of Ulduar. Of the four symbols, the most pleasing to the Mind-Seekers is evidently that of Mimiron: a gear. Players needed to draw this symbol of ingenuity with the lights in order to progress.

Observant players also noted that, of the four symbols, only the gear is symmetrical across both axis. As the Mind-Seekers never specified which direction was "up" on the lights puzzle, it was a good guess to assume it needed symmetry. Well done! - Developer note

A gear, the symbol of Mimiron, the most intellectual keeper. - Muffinus (https://twitter.com/Muffinus)

Step Two: Mindcraft

Its time to travel again: Ruins of Ahnquiraj 40. Make your way trough the whole raid, behind C'thun, the last boss of the raid instance, past the 3 NPCs, at the top of the stairway is an alter with an Mind Larva on it.

1000 years imprisoned.
Surely it wears on the mind.

Click on the orange glowing insect to start Mindcraft. A Minigame similar to Jewelcraft.
Match five brains in a row to win!

1000 years imprisoned.
Surely it weighs on the mind.

This clue refers to the three dragons imprisoned with C’thun in the Temple of Ahn’Qiraj. Simply head to AQ40 and make your way to the end of the dungeon where C’thun resides.

There was no way we weren’t doing something in AQ40, and we’ve always wanted to use that space behind the dragons! - Developer note
Just before C’thun is a side path to the dragons. Behind them, at the top of a stairway, you’ll find an altar with a Mind Larva on it.

Interact with the Mind Larva to insert it into your brain, presenting you with a Jewelcraft-like match three minigame that will project in front of you (and anywhere you look). The key to winning the game, of course, is brains: match five brains in a row to win!

We wanted to put in an easier, more fun puzzle to give your brains a rest. What we didn’t count on was the win condition on this puzzle bring one of the most hotly-debated things in the Secrets Discord channel, even after players had long progressed past it! - Developer Note

Note number 3 - The Chair

Deeper than deep.
Awaits your seat.

You need to get a Shadowweave Mask to proceed. You can buy these either on the Auction House or, if you have the tailoring profession, craft it yourself (Pattern: Shadowweave Mask). The Pattern is obtainable from the Dark Iron Steamsmith.

Then move to Deepholm, enter the Crumbling Depth and interact with the Dark Fissure.

A fissure in the ground, barely wide enough to squeeze through. It's too dark to see anything, but you can tell that it is very deep.
Drop into the fissure.

WARNING: You are about to fall into a dark fissure. You may not be able to climb back out again. Are you very sure you want to do this?

Accept the warning and hop into your next adventure to explore the deep cavern. Find the chair with the Dingy Plague behind it. Equip your Shadowwave Mask, interact with the strange skull on the chair and a note will appear:

The plaque is old and barely legible. You can only make out fragments of each line of text.
Supremacy?
Get…
Shirk…
…eke…

Step 4: Its Binary?

Where the shaded delegate may appear.

Gnomes? Oh noes.
Enter Gnomeregan and go to the Engeneering Labs. You will find a wall with 10 numeric consoles and a plaque with instructions.

01110111 00100 10010110 10101
11110111 01100 01111111 01000
011010111001011010010110 10111101
11001 00111111 10010 01001001
10000 011010010110100111010110
01011011 11110 11110001 11111
11100000 00010 11111111 01000
10110111 10101 01111111 00001
10101110 11111 00110000 01000
101101010010101110010110
180
1111111111

Set the the consoles to 1222176597.

You can use the following scripts as macros:
Up: /script SelectGossipOption(1)
Down: /script SelectGossipOption(2)

Where the shaded delegate may appear.

The ‘shaded delegate’ refers to the Dark Iron Ambassador, a rare spawn that sometimes appears in the Gnomeregan dungeon. Deep within the grinding, gear-filled city, you’ll find a wall with a series of 10 Numeric Consoles, which allow you to enter a digit from 1 to 9. Above these consoles is an Instructions plaque, which reads:

A puzzle in binary? Not so simple. The binary was another red herring, and a very effective one at that. This puzzle also stumped players for over 48 hours, though it didn’t quite hit the insanity level of The Chair.

The binary is in sets of 8, 5, and 24 digits. 8s and 5s always appear as a pair.
For each 8-5 pair, take the sums of the digits in each side, and multiply them together.
Ex: 10010110 10101 = 4 and 3, and 4 x 3 = 12.
For each 24-digit entry, sum up the digits directly.
Ex: 011010111001011010010110 = 13.
That gives you the sequence 6 12 14 7 13 18 12 3 13 20 25 3 8 18 7 25 2 13.
Put that through a basic Caesar cipher (A=1, B=2, C=3, etc…): F L N G M R L C M T Y C H R G Y B M
That gives you abbreviated versions of three pet battle abilities found on Murloc pets: Falling Murloc, Mighty Charge, and Eye Beam.
At max level, these abilities do a total of 684, 560, and 1110 damage, giving us our code, 6845601110.
The ‘180’ near the end of the instructions tells you to flip it around (as in 180 degrees): 0111065486.
And lastly, +1111111111 is simple addition: 1222176597.
Putting 1222176597 into the Numeric Consoles will complete this puzzle.

The localization team was put to the test with this puzzle, as the solution doesn’t work in Traditional and Simplified Chinese. Both localization teams did a great job of coming up with their own puzzle, and the puzzle was first solved in Traditional Chinese! Enterprising players eventually worked the puzzle solution out in non-Chinese languages by working backward from the known solution! - Developer note

With the correct numbers entered, all the consoles close up and the next note appears.

Note 5: Nightmare Tumor

Boo. Go to Val'sharah, find the Nightmare Tumor and play the Eyecraft minigame where you'll have to uncross the optic nerves of Il'gynoth's many eyeballs. This minigame is similar to Blingtron's Circuit Design Tutorial.
Il'gynoth will whisper to you "AL'KSH SYQ IIR AWAN? IILTH SYTHN AQEV." which translates to "Is this real or an illusion? You are going mad."

/way Val'sharah 66.4 36.5

Games and toys are left behind.
When you awaken screaming.

This clue directs you to the Emerald Nightmare-affected areas of Val’sharah, where the Night Elves living there were driven from their homes by the Nightmare. In one particular home in Ash’theran, you’ll find a minigame, similar to the Blingtron's Circuit Design Tutorial minigame, which has been corrupted by Il’gynoth. The goal of the minigame is to uncross all Il’gynoth’s optic nerves by clicking on his eyeballs to swap them.

Meanwhile, Il’gynoth is reminding you that you are going “mad, mad, mad…”

And now, the fun part. Promise me that you wont throw your PC out of the Window, because thats what i was about to do:

Note 6: The Endless Halls - What you seek is buried within.

Secret-seekers, naturally, would seek the Tomb of Secrets (within the Valley of Emperors) in Kun-Lai Summit, wherein secrets are buried. There, you’ll find an urn you can interact with to consume the ashes of an evil sorcerer (seems like a good idea). When you wake up, you will find yourself in an endless maze.
We sought to create a puzzle that couldn’t be completed by just following a guide. Thus, the Endless Halls is randomized based on your player ID, as well as the day of the week. Very few players will ever see the same layout, and coming back the next day will present you with an entirely new challenge. - Developer note

Runes on this urn indicate that it contains some of the remains of a powerful mogu spirit-binder. Many of the markings appear to be warnings.

Consume the ashes.
WARNING: You are about to consume the ashes of an evil sorcerer. There is no way to tell what will happen. Are you VERY sure you want to do this?

The Endless Halls is an unforgiving labyrinth, purposefully designed to befuddle and confound at every twist and turn. You begin your journey in an unassuming chamber with murky pathways leading in the cardinal directions (North, East, South, West), though some are obstructed by debris. Venturing through one of these passages will obscure your vision momentarily, only to reveal you in an adjacent room.

The objective within this maze is to procure five distinct hues of orbs (red, blue, green, yellow, and purple) and transport them individually to their corresponding runes of the same color. Yet, numerous intricacies compound the challenge, rendering the task far more formidable than mere description suggests.

The maze is set on an 8x8 grid of rooms, each with between one and four exits. However, rooms with four exits are actually two interconnected two-way rooms, known as Non-Intersecting Cross rooms. These unique rooms contribute to the maze's disorienting nature and do not contain any orbs or runes.

Another source of confusion is the maze's edges, which loop around but not directly. Exiting one end of the maze will transport you to the other side with an additional offset, making it challenging to predict your destination. However, you can reliably backtrack from your new position to your previous one, aiding navigation.

Beware of the Teleportation Trap, a single room within the maze that secretly teleports you to a random location upon entry. Identifying and avoiding this room is crucial for progress.

Once you deliver the fifth orb to its matching rune, the next exit you traverse leads to a golden room with the next Inconspicuous Note, marking progress.

Reflecting on player experiences, developers acknowledge that placing the most challenging puzzle at the end caused players to trickle through the finish line, missing a collective celebration moment. They also note the variance in maze difficulty, ranging from easily solvable through random wandering to requiring meticulous mapping, leading to frustration. Future iterations will aim to address these issues, with gratitude to the community for suggestions, including adding jump scares. Additionally, they recommend using the Lucid Nightmare Helper-addon for assistance in retracing steps and mapping out rooms.

Note 7: The forgotten Crypt

The way is now open.
To the greatest secret never told.
A fitting end to your journey.

"The clue here is a reference to a place in the world that has long been a secret to those in the know, but has never been used—the horrendously creepy Forgotten Crypts in Karazhan. In the game since the WoW’s initial launch, exploration-focused players ventured into these crypts for years after each patch, in the hopes of finding some newly-added secret. They were perpetually disappointed—until now.

This time, sitting on top of a pile of bones near the bottom of this huge-but-empty crypt (within The Pit of Criminals) is a chest containing the Lucid Nightmare."

https://www.youtube.com/watch?v=H-mxmN5mwDs