Why this build
How the build works
This Discipline Priest build is about doing more with each point of mana. Mental Strength adds 10% Intellect, Meditation lets 50% of your mana regeneration continue while casting, and Mental Agility trims 3% off Smite, Holy Fire and your instants. Inner Focus makes your next spell free and adds 25% crit if it is a direct spell, which is best spent on Greater Heal.
The healing core is your instants. Twin Disciplines adds 4% damage and healing to instant spells, which covers Power Word: Shield, Renew, Shadow Word: Pain and Penance. Improved Power Word: Shield adds 20% to every shield. Holy Precision gives 6% Holy hit so Smite and Penance land more often on higher-level mobs.
Penance is the payoff at 30. It channels for 2 seconds and hits three times, either as Holy damage on an enemy or as a heal on an ally, on a 12-second cooldown. That gives you a burst heal for the tank and a damage spell while questing.
Consensus is low here: guides split three ways at level 30, and this is the version that reaches Penance.
Leveling tips
Wand Specialization comes first because a wand finishes most of your kills before 20. Twin Disciplines and Mental Strength follow, then Meditation at 20 to cut drinking breaks. Shield the pull, Smite, add Shadow Word: Pain if your mana allows it, and finish with the wand.
From 30, Penance doubles as damage or a self-heal. In dungeons, shield the tank before the pull and keep Renew rolling. Discipline is slower than Shadow solo, so if you only quest, Shadow is the faster choice.
Changes in WoW Forever
Penance, Twin Disciplines, Power in Light, Soul Warding, Renewed Hope and Divine Aegis are all new, and they turn Discipline into a real shield healer. On 15 Oct, Mental Strength moved to row 2 and now gives 10% Intellect instead of 15%, and Improved Power Word: Shield moved to row 3. On 30 Oct, Binding Heal became the passive Holy Binding in the Holy tree, so older guides that list Binding Heal in the rotation are out of date. All talent text here includes the Priest hotfixes of 30 Oct.
Toward level 60
The most-planned endgame build is 33/18/0: Soul Warding, Renewed Hope, Divine Aegis and Power Infusion in Discipline, plus Holy Specialization, Divine Fury and Inspiration from Holy. One guide prefers 31/20/0. Expect it to shift once healers reach the level cap.