Impact

Impact is a mage talent that gives each spell a chance to reset your Fire Blast and give it the ability to stun the target for 2 seconds and spread all damage over time effects currently on the target to any enemy targets within 12 yards.

Tips
Enemy spell casts may be interrupted (albeit somewhat unreliably) by using an impact proc.

Impact has a chance to proc off each individual tick of Arcane Missiles and Blizzard, however those spells will no longer cause a stun as previously.