Siffed (25 player)

Activate the hard mode of Thorim.

Before Thorim can be faught, part of the raid must run a gauntlet to reach him. After 3 minutes Sif despawns. After 5 minutes the raid is wiped. Normal mode requires engaging Thorim between 3 and 5 minutes after the encounter is started. Engaging Thorim in less then 3 minutes forces the raid to fight both Sif and Thorim simultaneously and counts as the hard mode of the encounter.

If at this point you wipe, you will still be granted the Heroic: Siffed achievement. If you manage to kill Thorim, you will also recieve the Heroic: Lose Your Illusion achievement.

Sif cannot be killed, but does attack the raid with Frostbolt Volley, Frost Nova and Blizzard. She also removes the Touch of Dominion debuff from Thorim, increasing his damage by 66% and his health by 43%.

as of patch 7.0.3 , the strategy is just the same... use the lever on your left , open the door and move around until you reach thorim... YOU MUST DO THIS UNDER 3 MINUTES ! after that he jumps down in arena while Sif is still present... nuke him down and farm all achieves including this one... hope it helps !

Was trying to down Thorim on 25-man normal mode last night. After several wipes, we decided to use the strategy of bloodlusting when the gauntlet group reached the 2nd mini-boss. Without even being able to down this in regular mode, we somehow activated this hard mode and of course, we wiped again.

The moral of the story is yes, you can activate hard mode and get this achievement without actually downing the boss or getting loot. It is a 2-part achievement, and the 2nd part http://www.wowhead.com/?achievement=3183 is for actually killing the boss.