Edit: this post fell sadly out of date when the talent trees were reworked for Wrath of the Lich King. It's now of minor historical interest at most. I'm working on a new levelling guide but Please check our my rough guide to shadow talents in the meantime.
I'm a firm believer that all talents are equal — but like the book says, some talents are more equal than others.
This progressive build is my favourite way to get from level 10 to 40. It's designed around mana efficiency and minimal downtime. The ultimate goal is shadowform at level 40.
To get the most out of it, you need to get used to wanding down your mobs for the last 30-40% of their health. This should be sufficient to take you out of the five-second rule and ensure you get the full benefit from spirit tap. With the right balance of intellect, spirit and stamina, you'll be able to keep going indefinitely, making you the envy of mages everywhere and even putting hunters to their shame.
Levels 10-14: wand specialisation (discipline tree)
It may seen counterintuitive to start a shadow levelling build in discipline, but this talent is one of the gems of any solo priest build, adding an extra 25% to your wand damage. You will be wanding a lot on your way to 70 so make the most of it. Some guides will tell you to take spirit tap first then come back for this. That's fine too, but I find at low levels spirit regenerates fast enough on its own and prefer the dps increase up front.
Levels 15-19: spirit tap
Spirit tap does two things — when you land a killing blow on a mob, it doubles your normal mana regeneration for 15 seconds; it also enables 50% of your mana regeneration while casting (i.e. when you are within the five-second rule). So whether you are resting or tackling adds, you gain mana. This is the primary reason why you want to prioritise spirit gear as you level.
Levels 20-21: improved shadow word: pain
This increases the duration of shadow word: pain by six seconds. This means you get two additional ticks of damage from the spell, increasing its overall damage by 25%.
Levels 22-24: shadow focus
Each point in shadow focus reduced your target's chance to resist your spells by 2%. Fewer resists equals less time casting and greater mana efficiency. Three points is enough to ensure your spells have the maximum possible chance to land on mobs up to two levels higher than you, which makes questing and grinding a lot easier and ensures you get more experience per kill.
Levels 25-29: blackout
Blackout gives all your shadow damage spells a chance to stun your target. It's not a critical talent for levelling but it's very sweet when it goes off.
Levels 30-31: shadow reach
Increases the range of your offensive shadow spells by 20%. This is the reason why we have waited until now to take the next talent, mind flay.
Level 32: mind flay
Mind flay is a channelled spell that does damage over three seconds and reduces movement speed by 50%. It's a priest's most mana efficient spell. The channelled nature means it can be interrupted by damage, but the snare effect works beautifully with psychic scream, enabling you to keep a feared mob under control while doing damage. However, the range of the spell is so low that this method only really works with shadow reach.
Levels 33-34: improved psychic scream
This reduces the cooldown of psychic scream by four seconds. It's not an essential talent, but it makes continuous grinding using the fear/flay method that much easier. It's also a requirement for silence later on.
Level 35: vampiric embrace
A core talent of any shadow build, this debuff returns 15% of your shadow spell damage as health to you and your party. While playing solo, it reduces your reliance on the expensive power word: shield and helps to passively top up any splash damage as you go.
Levels 36-37: improved vampiric embrace
Increases the health returned by the spell to 25%. This talent really begins to shine at 40 with shadowform, when your incoming damage is reduced by 15%. You can pretty much take a beating one-on-one without loosing health.
Level 38: silence
This spell is on a fairly long cooldown, and as such is not a critical talent. However, it's your only spell interrupt at a distance and comes in very handy when fighting casters. The silence lasts long enough to pull the mob into fear range, giving you a second interrupt.
Level 39: focused mind
As we're on a mana efficiency drive, where better to put a point than in a talent that reduces the mana cost of some of your spells? To be honest, it's a filler, but one point reduces the mana cost of mind flay, mind blast and mind control by 5%.
Level 40: darkness, shadowform
Shadowform requires 30 points in the shadow tree, so level 40 is the earliest we can pick it up. Unfortunately, five of our required points are currently languishing in the discipline tree so we'll need to respec.
Pick up the same talents described above and put your spare five points into darkness, which increases your shadow damage by 10%. Your final point goes into shadowform, and your build should look like this.
Congratulations, you have just increased your shadow dps by a whopping 15% with just one point. This increase also applies to shadow wand damage, so from now on it's worth trying to pick up only shadow damage wands.
The trade-off with shadowform is an inability to cast holy spells (essentially, just your heals, smite and holy fire), but with the damage multipliers on shadow spells from talents, you should never even consider holy damage again.
Unlearning your talents costs gold, and at level 40 you are probably saving up for your mount. If you don't have the money, it's not essential to respec. Simply put your next five points into darkness and pick up shadowform at 45.
So there you are: your first 40 or so levels as a shadow priest. This build won't top the damage metres but it is an incredibly efficient, effective build that will enable you to quest and grind swiftly and either heal or dps in groups as required. Next time, we'll take a look at later levels on the grind to 70.
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