As far as I know this only happens on trinitycore.
Needed:
#Horde
#WOTLK
#Level 80
1) Go to Dragonblight (Agamar's hammer)
2) Find the NPC: Koltira Deathweaver
3) Pick up the quest: In Service of Frost: http://www.wowhead.com/quest=12127
4) Use the following item: Frost Gem Frost Gem - Item - World of Warcraft on people with 35% or less health to kill them
Example:
http://img6.imageshack.us/img6/7792/fgem.jpg
Not Tried the unholy/blood gems but this works.
Enjoy.