Today's tip is brought to you by my wifes great idea.
This tip is for level 85 characters only. You must have unlocked the Fireland Dailes up to and including the Forlorn Spire or whatever it is called. After you do your second set of dailies, you get a quest to go into a cave and stamp out some blue runes. When you stamp out a rune, it kills a bunch of elementals that are attacking you. These will give you Grisly Trophies.
While you are standing in the rune, you take very little damage. You can stand there and build up your pile of guys until you are ready to blow it up. Continue on to each rune and do the same thing. After the final rune, abandon the quest if you do not have all 250 grisly trophies. Pick it back up, rinse and repeat until you have them all. It took us about 15 minutes with three of us in a group.