Note that this guide was for the WotLK patch pre-Cata! Some things (such as hit rating, enchants, etc) are no longer up to date! New guide forthcoming soon.

Please read this thoroughly before posting. Do post if you have updates/corrections -- initially information here may not be completely correct as it's basically from my own personal experience on PTR/beta.

I just logged in!
First thing, make sure you go to your priest trainer of choice and learn Mastery and Mysticism. These are both passive talents.

What should I spec?
3/0/31 with 2 points left over to personal taste. It should be obvious that the 3 points in Disc go in Twin Disciplines. Due to the slimmed down trees, you'll be taking most of the talents in Shadow, with the exception of Improved Psychic Scream/Phantasm/Silence/Paralysis/Psychic Horror.

What should I glyph?
Prime: Mind Flay, SWP, SWD
Major: Your choice here. None offer any DPS boost, so pick for utility.
Minor: Your choice here as well.

How much hit rating do I need?
446 or 17%. (edit: 420 or 16% if you're Draenei) Remember, there's no more Misery and no more hit debuffs on mobs. Also remember that you convert spirit to hit via the Twisted Faith talent, but only from gear and buffs, not from your base spirit pool -- i..e I have 297 hit rating from gear, and I get 168 spirit from gear, which converts into 168 more hit rating for a total of 465.

What's this reforging? Should I use it? What should I use it on?
It depends. Reforging allows you to convert 40% of an item stat on your gear to another stat that is not currently present on the item. For example, take Ring of Rapid Ascent. I can either convert 27 Crit Rating or 24 Haste Rating to 27 or 24 Spirit or Mastery. There's other options, but those are the only 2 that matter. Note that you'd never reforge into hit rating, as Spirit gives the same effect. Don't reforge into Mastery, it is terrible right now -- i.e. I'd only reforge that ring if I needed hit.

If you're over hit cap, reforge hit to haste seems to be the way to go, unless you already have an extreme amount of haste vs crit, then you'd want to reforge to crit. Note that in most cases you won't have a choice -- you cannot reforge to a stat that is already on an item. Therefore, an item like Amulet of the Silent Eulogy means if you want to reforge out of excess hit, you could only convert it to crit since it already has haste.

What does Mastery do?
As stated just above, it's terrible for shadow priests at 80. Read the tooltip on Mastery to see what it actually does though.

Should I regem?
If you're dedicated to purely min/maxing even for the next 2 months, then probably yes. Pay close attention to what gems are now. Runed Cardinal Rubies are now Brilliant Cardinal Rubies that are +20 Int. Remember that Int converts into spellpower now -- you won't see spellpower on gear anymore except for weapons, procs & enchants.

Red: +20 int

Yellow: +10 int/10 haste as long as socket bonus is better than (5 int? 5 sp? Pretty much any item for us has at least this bonus though so it's moot) Note that 10 int/10 crit may actually be slightly better depending on SWD spam sub 25%. From napkin math the difference either way will be small but worth mentioning.

Blue: Only match for socket bonuses to fit a meta gem, otherwise 20 int here. Or fit 10 int/10 spi if you are trying to reach hit cap. Note that you can use a Nightmare Tear (10 all stats) for one of these.

After regemming/reforging you should be as close to 446 hit as possible.

What's my spell casting/priority system now?
SWD makes a triumphant return!

Boss health>25%: Dots (VT/SWP/DP) are still top priority. After that, SWD on cooldown, then MB, then MF as filler.
Boss health<25%: Dots (VT/SWP/DP) are still top priority. After that spam SWD as health allows.

Spam SWD? Wha?
Glyph of Shadow Word Death: If your Shadow Word Death fails to kill the target at or below 25% health, your Shadow Word Death's cooldown is instantly reset.

This means it's a spammable instant once a boss reaches 25%. Note that you WILL kill yourself if you spam this with no regard for your health bar. SWD can crit upwards of 20k, and the backlash will be about half of that. VE is 15% self heal now.

Hotfixes have been coming fast and furious so our priority system is in flux right now. I'll update later once things have stabilized and we can settle on an agreed list.

DoT clipping changed
Previously, when you cast a new VT on a mob with an existing VT, a completely new VT was applied to the mob. So if you cast a new VT only a split second too early, you'd clip that last tick of VT and lose it.

That has changed. Now when you refresh VT/DP, it acts exactly as SWP has when Pain&Suffering refreshed it. The DoT's duration is simply refreshed, and the ticks continue to happen. What this means to the casual spriest is instead of trying to refresh VT/DP the instant after it falls, you want to try to refresh it exactly as it falls or slightly before. You still don't want to refresh it too early because you'd be wasting a GCD.

Other Misc Notes
Switch chest enchant back to 10 all stats from 15 spirit.

It is also worth noting that Damage of Time spells like Shadow Word: Pain, Devouring Plague and Vampiric Touch can no longer be clipped. Recasting the spell will simply refresh the time remaining on the debuff without interrupting the ticks.

Enchant Priorities will remain the same from 3.3.*, for the most part.

Weapon

Enchant Weapon - Mighty Spellpower
Enchant Staff - Greater Spellpower
Enchant Weapon - Black Magic

Helm

[Arcanum of Burning Mysteries]

Shoulders

[Greater Inscription of the Storm]

Chest

Enchant Chest - Powerful Stats

Cloak

Enchant Cloak - Greater Speed

Bracers

Enchant Bracers - Superior Spellpower

Gloves

Enchant Gloves - Exceptional Spellpower

Legs

[Brilliant Spellthread]

Boots

Enchant Boots - Tuskarr's Vitality

Belt

[Eternal Belt Buckle]

It is important to note that while the Engineering Glove enchant has been reduced from 340 haste to 240 haste, it will now stack with Enchant Gloves - Exceptional Spellpower. The same is true for Nitro Boosts, which will now stack with Enchant Boots - Tuskarr's Vitality. This also applies to Springy Arachnoweave and Enchant Cloak - Greater Speed.


Haste, DoTs and You in 4.0.1 and beyond

Below are the values of haste needed to add another tick to the damage over time spells we all know and love. These are only for the base spell and does not account for any change by talents and/or glyphs.


Vampiric Touch

Haste	Ticks	Haste Rating
0.0%	5	0
20.0%	6	656
40.0%	7	1312
60.0%	8	1968
80.0%	9	2624
100.0%	10	3279

Shadow Word: Pain

Haste	Ticks	Haste Rating
0.0%	6	0
16.7%	7	547
33.3%	8	1093
50.0%	9	1640
66.7%	10	2186
83.3%	11	2733
100.0%	12	3279

Devouring Plague

Haste	Ticks	Haste Rating
0.0%	8	0
12.5%	9	410
25.0%	10	820
37.5%	11	1230
50.0%	12	1640
62.5%	13	2050
75.0%	14	2460
87.5%	15	2869
100.0%	16	3279

Mind Flay

Haste	Ticks	Haste Rating
0.0%	3	0
33.3%	4	1093
66.7%	5	2186
100.0%	6	3279

(DISCLAIMER: Haste ratings are approximate.)

Gemming all Spellpower+Spirit purples into blue sockets to pick up the bonuses before you reforge to meet your hit rating might be more optimal.

As noted at the bottom of my post, this should be Enchant Chest - Powerful Stats. +10 int/+10 spi is now superior to +15 spirit.

Current numbers suggest that these effects are NOT carried over.

2 things here:

I tried this out last night and I'd like some input as to the viability of it: I would keep my dots up as I would do normally as well as spamming MB when applicable, however while my other dots were going, I would just keep spamming DP repeatedly for the instant damage. I would get on avg 4-5k per application of DP (each gcd) and would often times spike to ~9k or so for them. I only tried it out on 2 fights last night (HMarrow, RLDW) but it was producing somewhat similar dps to what I was outputting prior to this patch. What would the viability of this be (if at all)?

My 2nd point. Since Mindflay priority is now (according to the OP) last on our list, should we not be concerned with keeping 4pc T10 going into Cataclysm, and instead be gearing and reforging for best haste/crit once we've reached the hit cap? I have a lot of other gear that I COULD be using in place of a few pieces of T10 however up until this point I've been keeping with T10 due to how great the 4pc bonus was.

No, that is not going to do near the damage of a proper rotation. Just because it was more damage than last patch means nothing when you are comparing it with current data. The rotation/priority list in the original post by Snowy will do much more than spamming Devouring Plague would be. With regards to your second point the answer is again, negative. Mindflay may have a lower priority but it will still be the main filler while Mind Blast and and Shadow Word: Death are on cooldown (remember, dots will have a base duration, meaning it will be less frantic to keep them up) until 25%.

If there's adequate incoming healing, moving while spamming death should be preferred for the Shadow Apparition boost. I find myself only stopping for VT refreshes.

It appears mental agility effects all instant cast spells. I was thinking that during the burn phase wouldn't this skill be beneficial for a sw spam more so then what i consider pvp talents? I might be way off and i admit i have yet to raid and if that is so i apologize.
I have heard we have little mana problems but i would think this phase might provide one since we are not spamming MF and reducing the CD of shadowfiend.

Does anyone have logs of what type of damage throughput we are capable of? I have heard the stories of mages and boomkins being crazy but i am curious where we stand. I do not expect to be "sunwell'd" again but i am hoping we still have some of our glory.
( if this is the wrong area for this request please direct me to where i should present it. I was hesitant to post this at all.)

You should look at the talent "Masochism" and read it carefully.

I had 34% Haste upon logging out last night (Rounded up) I log in today and New Talents are supposed to give me 3% from Darkness & 5% from Shadowform but i still remain @ 34% - Did we lose 8% from somewhere else or are we bugged?