Slow

Slow is a talent-trained mage spell that slows movement and reduces ranged attack and casting speed for 15 seconds. It is a 60% snare combined with a 60% negative haste debuff that affects ranged attacks and a 30% for spell casting. Only one target can be affected by Slow at a time.

The Mages of Lordaeron have been able to create a spell that hinders both movement and reflex. By warping the very patterns of time that surround his target, Slow enables the caster to bring an enemy's offensive to a crawl. Time cannot be held in check by even the mightiest of Mages, however, so the effects of this temporal shift cease as the power of the spell wanes.

Talent improvement
The talent Nether Vortex (mage talent) gives Arcane Blast a chance to apply Slow to the target if no target is afflicted by Slow.

Tips and tricks
This is useful against most classes in PvP. For casters, the cast speed debuff is used similar to a warlock's Curse of Tongues, giving the mage a better window to interrupt with Counterspell. For melee classes, the snare is as effective as any frost-based snare, and the cast is instant, meaning it can be cast on the run to better escape. For hunters that can't be kited, Slow at least reduces their ranged attack speed.

This ability counts as a snare for the purpose of Torment the Weak, but since every tanking class also has a snare, it is seldom necessary in PvE.