Realm of Shadows
Instant 2-3min cooldown
Requires Death Knight
Requires level 92-100 / Talent
For short moment, you slip to the realm of shadows for 5 seconds. During that time, all your damage done is collected to your target debuff, which start dealing damage for 10 seconds, after you return from the Realm of Shadows. Also your damage taken during realm of shadows is converted to debuff, which start dealing damage to you for 10 seconds, after you return from the Realm of Shadows.
During on Wrath of the Lich King, we visited twice on Realm of Shadows on questing (Death Knights on start area and on Dragonblight), and I thought, would be a nice having Realm of Shadows making cameo, being unique ability which can work as a defensive and offensive cooldown, and being also double-edged sword, if wrongly timed. Debuff cannot be dispelled any means except immunity.