You're going to need the first quest of the shadowmourne chain: The Sacred and the Corrupt - Quest - World of Warcraft
1. Head to the cave where Light's Vengeance is located: Light's Vengeance - Object - World of Warcraft
2. Clear up all the zombies and past the RP until "Vegard the Unforgiven" spawns.
3. Cast control undead
4. He has a spell called "Vegard's Vengeance" with no GCD.
5. I'm not very good with macros so I haven't figured out how to make him cast it repeatedly in one macro(If you guys could figure that out it would be great), but I just used "/cast Vegard's Vengeance".
It does a *small* amount of damage, but it's spammable, and props to whoever has enough knowledge in macros to figure it out.