First of all this might not be an exploit but i didn't know were else to put it.
When u have the Reflective shield talent in the Discipline tree it works.
Reflective shield Dmges the target for 50% of the dmg he did to u while u were shielded.
lets say ur in arena, u shield urself and mind control one. then when u do Shadow word: Death against the other target in arena u will lose the MC but not only did u do lets say 1k with SWD, but because of the MCing u also deal 500 Dmg extra because of your reflective shield.
I don't understand why it does it, so i maybe thought this was an exploit..
Screenie:
P.S The dmg looks fake, but thats the Font i use, u can put in ur own dmg fonts with an addon :P
For the ones that are interested: xDamageFont | World of Warcraft Addons | Curse