I hope to help the Shadow Priest community with progressing through the heroic modes of Mogu'shan Vaults by sharing thing I found useful during my progression. In this guide I will give tips and tricks I found useful for maximizing DPS on Gara'jal the Spiritbinder on 25 man heroic mode. I am not saying that everything I recommend is good or optimal and I am open to suggestions. They do, however, work and took me through heroic modes. Some tips may not work for you due to your guild using a different strategy but I will try to keep it as general as possible and mention if the tips I give are specific for a special tactic. This guide assumes that you know how the fight works.
Glyph of Mind Spike
I use this glyph for all fights where I use FDCL.
Glyph of Mind Flay
Good for when you move to totems.
Glyph of Fade
When you get Voodoo Doll, you can use this to reduce damage from minions. Use this with Phantasm to make you immune to ranged attacks for three seconds.
This is used to avoid damage from minions when you have Voodoo Doll and during sub-20%.
From Darkness, Comes Light or Mindbender
Personally I prefer From Darkness, Comes Light. It feels much more versatile than Mindbender and helps to burst down adds in other realm. Mindbender is more consistent damage on boss and I have heard that it lines up nicely with when you are leaving the other realm and have the damage buff up.
Use this as soon as you enter with a totem. This will make it easier for healers as everyone is low when you first enter.
Twist of Fate
You will have insane uptime on this due to the adds downstairs and the totems.
Halo or Cascade
I think Halo wins out during progression. It does more damage on boss and it does very nice damage on adds downstairs. Cascade is easier to use and does more damage downstairs because you can use it twice if you pop it as soon as you enter with your totem. I would pick Halo for progression, Cascade for cheesing damage.
General Tips and Tricks
This depends on if your guild uses Bloodlust/Heroism at start or not but if they do, I usually open like this:
What I like about this opener is that you will get a lusted Shadowfiend, your trinkets will probably proc before you throw dots up and you will get lusted dots too. Ideally, you should try to get your three orb Devouring Plague before trinket procs fall off and Shadow Word: Pain should be about to expire as your procs fall off so refresh that before they do.Potion
Shadow Word: Pain
I really recommend dotting totems as soon as they spawn. I do not care if I am not on the totem, I still dot it. It will help you proc Twist of Fate and it will help you proc From Darkness, Comes Light. It will boost your damage on boss. Also, make sure you are casting a Mind Flay when the totem is about to hit 20% and spam Shadow Word: Death on the totem. This will give you extra orbs and proc Twist of Fate in case your dots do not. The reason for casting Mind Flay before totem drops below 20% is to not get GCD locked because the totem will die very quickly in most cases and if you are GCD locked when it hits 20% you are probably not going to get your Shadow Word Death off.
Maximizing damage in Shadow Realm
I think most people just forget about their spell priority when they need to multi dot a lot of targets. You must remember to use Mind Blast on cooldown. Shadow Word Death is insanely strong here. It will give you Twist of Fate and orb. Use it whenever you can on low HP adds. If you took Halo, use it when it is ready. If you took Cascade, make sure you have it ready when you are about to enter Shadow Realm.
If you are not casting Mind Blast, Halo/Cascade or Shadow Word Death, just throw Shadow Word Pain up on high health Shadowy Minions. Do not waste dots on adds you think are going to die or who are at like 60%. Shadow Word Pain is only strong if it can tick for its full duration, else Vampiric Touch is probably better. Now, depending on how much you struggle on Enrage, you can save your Shadow Orbs for when you get to the normal realm and use it on boss. Else, use it on high health adds downstairs. As you are about to leave Shadow Realm, try to get some Shadow Word Pain on adds that are at like 20-40% health. Twist of Fate will still proc when you are in normal realm if the adds in Shadow Realm drop below 20% and your Shadow Word Pain is still on them.
Severer of Souls are highest priority. Put both Vampiric Touch and Shadow Word Pain on them. By putting Vampiric Touch you should not have any mana issues during the fight.
You can only use Shadowfiend twice on this fight, once on the pull and one more later on in the fight. I recommend using it when you are using your second potion, which should be when your trinket procs when boss is under 20% or about to hit 20%. This is also usually the point where a second Bloodlust/Heroism is used for people that died during the encounter.
Best cast bar for Shadow Priest. Gnosis is the only cast bar being able to show ticks of your Mind Flay properly. There is no excuse for using any other cast bar.
Tidy Plates (http://www.curse.com/addons/wow/tidy-plates)
Extremely useful for cleaning up your nameplates and makes it easier to track dots on many targets.
Buff and debuff timer(s)
Use whatever you feel comfortable with. I personally use WeakAuras but most addons work as good.
This is a video where you can see me using most of the tips I outlined in this guide. There are mistakes as expected from a first kill but I hope you can look past them. Do not take the damage meter for anything regarding raid DPS, it does not work on this fight due to phasing.
I hope you found the guide useful and that it will help you with your progression. If you do not agree with any of the things I mentioned, I am open for discussion. Please do leave feedback on how I can improve the guide and if you wish to see more guides like these.