Increases damage of all spells against targets with less than 35% health by X%.
Molten Fury is a mage talent that increases damage done to targets with less than 35% health by 6% per rank, up to 12% at max rank 2. This talent provides a straight 12% DPS increase for the last one third of a mob's health, for an overall DPS increase of 4% on average. The talent is popular among Fire-specced PvE raiding mages. The last 35% of a raid boss fight can be the most critical, with low mana and dead players. By the 35% mark, aggro is firmly established and DPS classes are free to unload, making the effective DPS increase much more valuable. Also, because this is a multiplicative damage increase, it increases more effectively as other vulnerabilities are applied to the target (such as Improved Scorch and Curse of the Elements) as well was gaining increases from talents such as Playing with Fire and Fire Power.
Although this talent is situated in the Fire tree it applies to all spell damage caused by the mage.
Besides boss fights also consider using this talent in a Blizzard build, where the gradual decrease in mob health increases your effective kill speed by 4% in the optimal case (12% * (35/100)).
Before Patch 3.0.2, this talent only worked below 20% mob health, but the bonus was of 20% extra damage, roughly the same overall as now.