Frost, Unholy Harnesses the energy that surrounds and binds all matter, drawing the target toward you.
Blood Harnesses the energy that surrounds and binds all matter, drawing the target toward you, forcing the enemy to attack you, and increasing threat you generate against that target by 200% for 3 sec.
Gripping a target will interrupt any cast currently in progress. This can be used to great effect in PvP, interrupting healers or preventing node captures. Casting will be interrupted even if the target is barely moved, such as when engaging a caster at point-blank range.
Tips and tactics
This is a great way to make your group like you. Caster mobs are difficult for a tank to deal with. Stand next to the tank and grip the caster over. Then switch to another target, letting the tank's AoE abilities build threat on the caster. It's now safely tanked.
Using Death Grip on a warrior with [Spell Reflection] up will send you hurtling towards the warrior instead of the warrior hurtling towards you.
On initial release this ability could not be used while moving. Undocumented change was made approximately 12/2/2008 to allow use while moving.
If two death knights Death Grip each other simultaneously, they will be pulled to each other's previous location.
A bug was discovered, and now long-since fixed, that if a death knight Death Gripped a player from the dock in Booty Bay onto the ship to Ratchet the person gripped would fly through northwards underneath the map, passing beneath Stormwind and eventually land on a ship underneath the game map.