Arcane Missiles is a mage ability learned at level 24 for those who have chosen the Arcane specialization. It is a channeled spell that shoots a series of missiles at the target, one wave each second over a period of time, dealing direct arcane damage.
Arcane Missiles has a chance to be activated after every damaging spell cast.
It will generate an [Arcane Charge]; while at least one charge is available, it will increase Arcane Missiles' damage.
Unlike other channeled spells, each second (or "tick") is considered a separate direct damage missile which passes through the normal direct damage checks (crit, resistance).
An often overlooked PvP benefit is the rapid speed with which it hits opponents causes regular spell interruption. Between this and [Slow], an Arcane mage can make it exceedingly difficult for an enemy player to get off spells with a cast time.
A notable effect of the fact is that "on spell hit" abilities, such as Mark of Defiance, can proc off each missile, similar to "on spell crit" abilities. However, "on spell cast" abilities, such as Mystical Skyfire Diamond, only have a chance to proc on each casting of the spell, not on each bolt.
This spell can also be useful against rare enemies who are immune/resistant to both Fire and Frost damage. One example of those is the Boiling and Scalding elementals in Thousand Needles, immune to Frost and highly resistant to Fire.
Patch 5.2.0 (5-Mar-2013): Arcane Missile's damage has been reduced by 22.1%.
Patch 4.1.0 (26-Apr-2011): Arcane Missiles damage has been increased by 13%.
/Patch 4.0.1 (12-Oct-2010): This spell has been changed to proc on a 40% when casting spells. Mana cost removed.
Patch 3.2.2 (2009-09-22): Casting this spell while both Missile Barrage and Clearcasting are active will cause only Missile Barrage to be consumed.
Patch 3.0.8 (2009-01-20): This spell now only has one chance to trigger Arcane Concentration.
Patch 3.0.3 (04-Nov-2008): Reduced the mana cost of Fireball, Frostbolt, Frostfire Bolt, Arcane Blast, Arcane Missiles, and Arcane Explosion.
Patch 2.3.0 (13-Nov-2007): Players will no longer get strange error messages when casting this spell at evading targets. The spell will simply fail.
Patch 2.1.0 (22-May-2007):Spell haste now affects channeled spells such as Arcane Missiles, reducing the overall channeling time but still doing the same amount of damage, thus increasing the DPS. A bug was fixed where Arcane Missiles would fire an inconsistent number of missiles. This was fixed so that ranks 3-11 would always fire 5 pulses.
Patch 2.0.3 (09-Jan-2007): Mages will no longer see line of sight errors if the target moves behind an obstacle after the spell "Arcane Missiles" has begun casting.; "Arcane Missiles" will no longer continue to channel after the target is dead.
Patch 1.8.0 (10-Oct-2005): Should now properly report the correct "out of range" indicator on the action bar.
Patch 1.3.0 (07-Mar-2005): Fixed a bug where the spell would not function properly against spell-reflecting targets.