Torment

Torment is a Priest ability, available if they specialize far into Unholy.
http://images4.wikia.nocookie.net/__cb20080805054205/wowwiki/images/thumb/1/11/Spell_shadow_painandsuffering.png/32px-Spell_shadow_painandsuffering.png Torment
You apply a curse to the target, preventing from using the ability they just used for 10 seconds. If the enemy forces it, they take 5% damage.