Why this build
How the build works
This Arcane Mage build is built around one loop. Arcane Blast stacks up to four times; every stack gives you 12% of your Intellect as Spell Damage for 18 seconds and doubles the mana cost of the next Blast. Arcane Wrath is the payoff: it hits for 122 to 146 Arcane damage plus Spell Damage equal to 5% of your maximum mana, and it benefits from the stacks you have built.
Everything else keeps that loop affordable. Arcane Concentration gives every damage spell a 10% chance to make the next one free, and Missile Barrage gives Arcane Blast a 40% chance (20% for Arcane Wrath, Fireball and Frostbolt) to turn your next Arcane Missiles into a free, half-length channel. Improved Channeling makes Arcane Missiles immune to pushback and gives Blast and Wrath a 70% chance to keep their cast time when hit, which matters because you will be taking hits while soloing. Arcane Meditation lets 50% of your mana regeneration continue while casting, and Arcane Impact adds 6% crit to Arcane spells.
Leveling tips
Spend levels 10 to 14 on Improved Channeling and 15 to 19 on Arcane Concentration. Arcane Blast comes at 20, Missile Barrage right after. Arcane Wrath needs 15 points in the tree, so it arrives at level 25; until then, finish targets with Fireball or Frostbolt, which can also proc Missile Barrage.
Do not chain Arcane Blast past what the fight needs. Four stacks cost a lot of mana, and on trash that dies fast you are better off with two stacks and Arcane Wrath. Drink between pulls; Arcane runs out of mana faster than Frost when procs are cold. In dungeons, Arcane Explosion is your pack damage, and Arcane Subtlety is worth considering if you keep pulling threat.
Changes in WoW Forever
Arcane is a different spec from Classic. Arcane Blast, Arcane Wrath and Missile Barrage are all new. The 28 Oct hotfix reshaped the Mage trees: Arcane Focus was removed and Missile Barrage moved to row 2. On 30 Oct Arcane Blast was changed again to its current +100% cost per stack with an 18-second duration. Guides written before these dates may list talents that no longer exist, so check names before copying an older build.
Toward level 60
Provisional. The most planned level 60 build is deep Arcane: Arcane Mind 5, Arcane Instability 3, Presence of Mind and Arcane Power, with about 10 points in Fire for Incineration and Accelerant (which now also speeds up Arcane Wrath) and 3 in Precision for hit. That reflects what players are planning in calculators, not tested results, and the Mage trees have already changed twice this month.