Biggest CC Exploit Ever? Death Knight (Patreon)

I recently discovered the following exploit and (obviously I'm biased) but it feels like the strongest ever cc glitch I can remember apart from methods to actually disconnect players - which are in any case often impractical to use.

In the sixth row of the talent tree on the right-hand side is an ability called "Grip Of The Dead". This causes any enemy npc or player stepping into the death knight's death and decay to suffer a mobility loss of 90% decaying by 10% for 10 seconds. This is quite a powerful ability in itself and has uses in most competitive forms of wow.

However if you take the talent "Death's Echo" you get two charges of death and decay and can cast them back to back. If you leave a small delay of around half a second between overlapping uses of death and decay the following strange things happen:

1. You get the initial effect of death and decay as normal.

2. The effect then persists a little longer than 10 seconds at 10% movement reduction.

3. The effect then vanishes and returns for a second at 10% movement reduction.

4. The effect then vanishes again and returns for a full 10 seconds at 90% movement reduction with no reduction in movement speed below 90% during the whole 10 seconds. *

This is a very strong glitch and can trivialize any pve or pvp scenario against multiple enemies.

Sometimes the glitch does not work as intended and the movement reduction effect is still extended by 10 seconds but only at 10% movement reduction. This is still quite useful but not as game-breaking. This seems to be related to some timing effect.

*I have tested this on my characters to make sure it wasn't just a tooltip error-the effect is real. It is like trying to move through lots of treacle.