Orchestra of Masks

Achievable this week (week 2 at time of writing) of Horrific Visions Revisited. Done as Hunter, probably easier as Demon Hunter.

Here's a link to a run I did as a geared blood DK - Orgrimmar, Stormwind. Gear makes this vastly easier, and being a tank or sturdy melee also makes things easier. I didn't use consumables, but you obviously could to get a bit of an edge.

General tips

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• Farm nemesis (Gammon/Hogger). His +150 sanity restore is incredible. You can and should play around this - if you need sanity, check how many mobs it is until nemesis spawn, and consider whether you have time to kill them and get your sanity up that way. You can even farm nemesis for sanity gain (killing 25 mobs and the nemesis is nearly always going to be far faster than you'll passively lose 150 sanity).
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• As obvious as it sounds, learn the boss and miniboss mechanics. None of them are crazy, but they can be pretty unforgiving, and not always telegraphed to allow you to just respond to them - I would suggest that reading the wowhead article for Orgrimmar or Stormwind is a good start, along with watching a POV, to specifically look at the big sanity loss mechanics. Most bosses have a frontal of some description, if you forget what a cast does during the run, defaulting to a sideways move isn't a bad idea.
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• Play into your cooldowns. Very little trash causes you to lose sanity (in fact, as mentioned with the nemesis spawns, you usually gain), so don't be afraid to sit on your CDs to make sure you have them up for the threatening boss encounters with big sanity loss mechanics. In the Orgrimmar video linked, you can see me do some slightly odd pathing in Valley of Honour, and take a ~25 second AFK in front of Thrall - I'm just waiting for cooldowns.
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• Orbs entirely block madnesses. You can use orbs during combat and during bosses. This can be helpful with scary overlaps. For example, Rexxar's boars knock you back as they spawn, which can punt you directly through split personality - which can be really rough, and can feel pretty unfair. You can throw down an orb at the right moment to prevent split personality from spawning entirely while you deal with the boars.
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• If you immune split personality's debuff and run through them, they despawn. You can see me doing this with AMS regularly, but other classes have ways to make this happen.
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• Track which potion restores sanity. The sanity loss potion is next to an NPC with a note - in Orgrimmar, they are located in the hut behind the bank (you can see me check this right at the start on the video), in Stormwind they're slightly forward and to the right, out in the open, after you spawn. You can then use something like this weakaura to tell you which is the good potion. Personally, I don't bother with the other buffs, because their effects are minor and they do something nasty when they expire - but if you're willing to spend some time tracking them down and extending their buffs, it may help slightly.
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• This will get easier. At time of writing, this is week 2 - we don't have all of the talent points yet, and there's some powerful stuff to come, so if you're struggling, give it a try in a couple of weeks.
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Orgrimmar tips

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• Melee can stand directly under Inquisitor Gnshal to not get hit by his Void Torrent. You can also line of sight it behind the tree, or use an immunity - in the video above, I AMS the second, which cancels the cast entirely.
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• Voidcrazed Hulk has a completely unavoidable sanity loss mechanic - you really want to nuke him down, if he gets more than 2 casts off you'll be in rough shape. Feel free to use lust/drums/combat pot here if needed.
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• Coagulated Horror has very quick mechanics - quick enough that you can't just react to them spawning, you need to be in motion as they cast.
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• Thrall's main gimmick is that he will regularly follow a cast up with a frontal which will drain a ton of sanity if you get hit. So while dealing with any other mechanic, from Thrall, keep an eye on him to see if he's casting. You have masses of time to respond to most of his other mechanics, it's the follow-up punch of Seismic Slam which will cost you runs.
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Stormwind tips

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• Patience is key on Stormwind bosses - Alleria, Umbric, Ul'rok and Shaw all have mechanics that might cause you to lose DPS/uptime - and that is completely fine.
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• Umbric especially will channel at the end of the room. Pets will interrupt him (and trigger him to channel on you), as will reaching him - so you may even want to wait for a few seconds if your interrupt is on cooldown.
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• You can really easily farm your sanity back up on Crawling Corruption in the mage quarter - there are so many of them you can spawn multiple Hoggers if needed. Use them between portals if you're missing sanity.
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• Alleria's main mechanic is void eruption - line of sight this behind the pillars, don't greed it.
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Completed this today in Visions of Orgrimmar as 666 ilvl Fury Warrior, Slayer talented.
Main reason for swap was bladestorm tech (that literally let's u ignore poison from mobs before Rexxar - which was greatest showstopper for me as the 2nd last pack stunned me instantly 99% of time).
Last pack before Rexxar (with the guy hidding in the fog) skipped via Heroic Leap - had to go back on foot, but it was worth anyway.
Made some mistakes, but still finished with 1 orb, just make sure you play a little with Nemesis Sanity gain (you can skip some entrance mobs and then get them later for Gamon spawn).

Keep it slow and surely, my general advice.
Left 2 wings are quite easy, just remember to dodge annoying mechanics (don't wait until last second as they will hit you most likely).
Cheers