So basically, in the Lich King fight there is this spell called Necrotic Plague. Necrotic Plague - Spell - World of Warcraft
"Infests the target with a deadly plague, causing 50000 Shadow damage every 5 sec for 15 sec. If the target dies while afflicted or the effect ends, this effect will gain an additional stack and jump to a nearby unit. If this effect is dispeled, it will lose a stack and jump to a nearby unit. Whenever this effect jumps, The Lich King's power will increase."
While wiping on the Lich King today in 10man, we were ending the raid, but we decided to just pull him and have some funnies. The mage loaded up a portal to Dalaran so we could click it to avoid repair bills, since we were just messing about really. Now, just as I was about to click I got this fancy Necrotic Plague on me. Naturally, it sticked on me after portal ended, and after it destroyed me, it jumped to a random guy which was next to the innkeeper. He was destroyed aswell.
It kept jumping around like that for a while, killing people and giving people a fun time.
Not really a exploit, but you could do some serious damage with it I suppose.
I didn't fraps it, but we are going ICC10 tomorrow and I will make sure we do it again and then fraps it, should give some lols.
Incase you didn't understand, think mana bomb from Doom lord Kazzak back in TBC, or Hakkar blood thing in Vanilla.