1) As Blood spec, take the dancing rune weapon talent
2) get to full runic power
3) Pull lots of mobs.
4) Pop DRW and spam Pestilence (nothing else, just pestilience).
5) the dancing rune weapon will copy it, but it does massive damage! (it does more damage depending on how many mobs you pull, so if you pull 50 mobs it will do insane damage)
^_^
Found on the eu wow forums earlier