Full: Shatter a Mirror of Ice. All foes near you and target ally take 15...59...70 cold damage and move 66% slower for 2...5...6 seconds. If you strike a foe hexed with Water Magic, Mirror of Ice recharges 50% faster.
Concise: Deals 15...59...70 cold damage and slows foes by 66% (2...5...6 seconds). Hits foes near you and target ally. Recharges 50% faster if it hits a foe hexed with Water Magic.
The damage is only applied to the target of the hex. Therefore, this spell has no effect on Frozen Burst.
Conditional hex spells like Freezing Gust deal the Mirror of Ice damage regardless of whether the hex was applied. Furthermore, Shard Storm will trigger Mirror of Ice whether the projectile from it hits or not.
The damage from Mirror of Ice is armor ignoring cold damage.
Historical note: Before the August 7, 2008 update, this skill was radically different, reflecting damage upon being the target of a spell rather than enhancing the caster's damage.