Ignite

Ignite is a passive mage talent that causes all critical hits from your fire spells to add a DoT to the target causing significant damage over 4 seconds. The DoT damage is a percentage of the spell's direct damage, up to 40% at rank 3. At max rank, this talent effectively makes the critical strike bonus for fire spells 110% (making critical strikes hit for 210% of normal damage), although not all damage is done up front. This is one of the most important talents in a fire mage's arsenal.

Known bugs
Sometimes a single tick of Ignite will do its damage and then also be added to a second Ignite if it lands just before the tick. This means that one or both ticks of Ignite can do twice the expected damage. This is often mistaken to mean the old "rolling" ignite system from pre-2.0 (see patch changes) is still present. The condition for this bug seems to be precise timing, making it difficult to exploit to any advantage.

Another bug occurs when two Fire crits land nearly simultaneously. Both crits should Ignite, but only one will take effect. To trigger this condition, cast an instant such as Fire Blast just as a projectile spell such as Fireball is about to land. This frequently affects elementalist mages who often double-crit with Shatter.

Both conditions can be explained by the theory that the critical strike and damage calculation is done at the time mana is spent and the spell leaves the hands, but the damage is done and Ignite applied to the target after projectile travel time. When a Fireball that will crit leaves the mage's hands, a new Ignite DoT is calculated from the computed damage and any current Ignite stack present on the target. This new Ignite DoT then overwrites the current Ignite when the spell lands, with a new 2 second counter. In computer science terms, this may be considered a race condition.

Consider the case where extra ignite ticks are appearing. The goal here is to time a fireball cast so that Ignite ticks on the target while a Fireball is mid-flight. In this case, a Fireball travel time of 1.0 seconds is assumed.


 * 0:00.00 - Mage begins to cast Fireball.
 * 0:03.00 - Fireball cast complete.
 * Spell is a crit, damage calculated at 2000.
 * Ignite is calculated at 800
 * 0:04.00 - First fireball lands, dealing 2000 damage and applying a 800 Ignite.
 * 0:04.50 - Mage begins to cast second Fireball.
 * 0:06.00 - Ignite ticks for 400.
 * 0:07.50 - Fireball cast complete.
 * Spell is a crit, damage calculated at 2000.
 * Ignite is calculated at 1200 (800 plus the 400 still remaining on the target)
 * 0:08.00 - Ignite ticks for 400.
 * 0:08.50 - Second fireball lands, dealing 2000 damage and applying a 1200 Ignite.
 * 0:10.50 - Ignite ticks for 600.
 * 0:12.50 - Ignite ticks for 600.

Total crit damage is 4000 while total Ignite damage is 2000, which is 10% more than expected. The Ignite tick at 8.0 was included in the second Fireball's new Ignite, but ticked anyways because the Fireball was still in flight. Now consider the case where two crits land but only one spell's Ignite is applied. A Fireball travel time of 1.0 seconds is assumed.


 * 0:00.00 - Mage begins to cast Fireball.
 * 0:03.00 - Fireball cast complete.
 * Spell is a crit, damage calculated at 2000.
 * Ignite is calculated at 800
 * 0:03.50 - Mage casts Fireblast (instant, no projectile time)
 * Spell is a crit, damage calculated at 1500.
 * Ignite is calculated at 600
 * 0:03.50 - Fireblast lands, dealing 1500 damage and applying a 600 Ignite.
 * 0:04.00 - First fireball lands, dealing 2000 damage and applying a 800 Ignite.
 * The Ignite from the Fireblast is simply overwritten.
 * 0:06.00 - Ignite ticks for 400.
 * 0:08.00 - Ignite ticks for 400.

Notice that the Fireball Ignite was not able to include the Ignite damage from the Fireblast because it was not present at the time the spell was completed. Also note that the Fireblast Ignite was not able to include the Ignite from the Fireball because it had not yet landed on the target. Thus, the Ignite from Fireball is overwriting the Ignite from Fireblast without including it.

These examples assume perfect timing which is almost never the case given client/server latencies, but the effects have been observed on live realms.

Ignite Munching
When Ignite damage is lost due to the behavior described above, it is sometimes called "Ignite Munching" by players. It is more of a serious problem with deep-fire mages since WoW 3.0 due to new talents Living Bomb and Hot Streak which can both cause extra fire crits (and thus ignites) while a projectile spell is still in flight.

In the case of Living Bomb, when the explosion at the end crits while a Fireball of Frostfire Bolt crit is still in flight, the Ignite from the Living Bomb explosion will be munched. In the case of Hot Streak, if the mage fires the instant Pyroblast immediately after a Fireball or Frostfire Bolt, and if both are crits, the Ignite from the Pyroblast will munch the Ignite damage from the first spell.

Some Ignite munching can be avoided by using particular spell rotations that take it into account. When Hot Streak procs, one trick is to cast the instant Pyroblast after a spell with no travel time, rather than after a Fireball or Frostfire Bolt which have a travel time. One possibility is to continue casting Fireballs/Frostfire Bolts until Living Bomb explodes, then put up a new LB before firing the instant Pyroblast. The global cooldown needed to put up LB is enough time for the last projectile to land, and the Pyroblast will not munch any Ingite if it crits. Do this only if Living Bomb has very little time remaining, as waiting too long to use a Hot Streak proc may cause you to lose a chance at another proc.

A second possibility is to use Scorch before instant Pyroblast. The Scorch cast time is long enough to allow any Fireballs or Frostfire Bolts to travel to their target, so if it crits it won't munch any ignites. Also, it has no travel time of its own, so it's crit won't be munched. And finally, it will refresh the Improved Scorch debuff on the target (Assuming the mage has this talent, which most deep-fire mages do). This bug in the ignite mechanic has given scorch a synergy with Hot Streak, however this synergy is by fault and not by design.

Partial Spell Resist
As of patch x.x there is a known issue with partial spell resists affecting the Ignite component unfavourably.

This is a bug Blizzard has acknowledged but stated they won't fix before the release of Cataclysm, when the ignite mechanic itself will be changed entirely.

The bug affecting ignite relates to the direct fire damage and the subsequent ignite tick(s). The direct fire damage hit is, like all damage spells, subjected to the effects of a partial spell resist roll. However, here's the rub, once that spell resist is calculated and applied to reduce both the direct damage hit and it's resulting ignite component, these already reduced ignite ticks are then themselves further subjected to another pass of the same spell resist roll each tick. In effect the ignite component is being penalised twice, once on the direct hit calculation and then again on each tick. This is often referred to as double dipping and has a noticable effect on the ignite damage being lost to partial resists.

(If anyone knows whether or not this bug has been fixed, please update here.)