Solving the Mystery (Horde)

Want to provide an update to this quest as some information is a little outdated.

-The fight starts with the NPC flying down from the rafters to the arena floor.
-NPC reveals himself to be Xan-Sallish, an Ethereal.
-Once he lands, he begins to monologue for about 8 seconds.
-Contrary to a previous comment, I started DPS immediately once he started talking. This did NOT cause the fight to bug out at the end.
-It follows the typical enrage timer for most brawls, with you getting a warning at the 1 minute mark.

Xan-Sallish uses 3 abilities in the fight.

-Consume Essence is interruptable, and should be done every time.
-He will then cast Rift Walk, which places a giant purple swirl on the ground, need to run away from it.
-Finally he casts an AoE Orb Storm, which spawns multiple orbs around him and shoot away from him at moderate speed.

It is a very easy fight, however the mechanics are important as either Rift Walk or Orb Storm will easily do 50-75% of your hp in damage.

The fight rewards a 'Mystery Satchel' that gives Shadowscrawled Tome as a reward.
It has a bit of lore:

You are my eyes when my eyes are elsewhere. See everything. Remember, record, report. The way they move, the way they fight, their choice of armor, their taste in weapons. Let no detail elude you.

Pay special attention to the heroes, the champions, the movers of fate. Watch from afar. Watch when up close. Interfere, if you deem it necessary.

Do not fail me, Xan-Sallish. Know that I have eyes on you, too.

-Shadreen

You turn the quest in and are rewarded with Bruce as a mount.

Excellent quest line, 10/10, would Brawl again.

I couldn't accept the Quest at first, it just said "Solving the Mystery failed." in chat. It turns out this was because you can only have one challege card in your inventory at a time, it worked after I deleted my other one.

*Spoilers !*

Upon Completion, the quest givers says:

I was there, <name>. I saw your fight.

We've had our suspicions about this "Watcher" character since the incident in Quel'Danas. It seems the rumors are true. They are watching us.

I'll relay the information to the correct authorities. Meanwhile, Boss Bazzelflange and I have arranged for a suitable reward for you. I hope you find it to your liking.

The incident in Quel'Danas is referred to the rare event that Shadreen, the Watcher, appears at the end of the Trial of Style and discusses with the blood elven presenters:

Shadreen says: Have you gathered the information I require?
Nastasia Flairwatcher says: Yes, here are the results.
Shadreen says: ...you have done well. My master shall be pleased to see this.

This dialogue is played and then they leave.
To be honest, the entire questline, along with this event at Trial of Style, seems to be inspired by the Facebook's data incident. I see few parallels at least ,goofy and funny activities that serve an ulterior , darker, data-collecting purpose.