Tranquil Master

Since the NPCs are not linked yet here the full list and where you can find them:
[npc=56439] is the last boss of the dungeon [zone=5956]. You must kill him on Heroic difficulty.
Sha of Violence is the third boss of the dungeon [zone=5918]. You must kill him on Heroic difficulty.
Sha of Anger is a rare world boss found in Kun-Lai Summit.
[npc=59651] is a NPC you have to kill when on the quest In the House of the Red Crane in Krasarang Wilds.
Sha of Hatred is a NPC you have to kill when on the quest The Sha of Hatred in a cave in Townlong Steppes.
Sha of Fear is the last boss of the raid [zone=6067]. You can kill him on normal or Heroic difficulty to get credit.

Edit: Fixed Sha of Anger zone.

I must admit I admire the symmetry of this achievement- it requires 2 dungeon bosses, 2 raid bosses, and 2 quest mobs at the ends of questlines.

the LFR version of Sha of Fear does not seem to grant credit for this achievement. when they say "normal or heroic" they really mean it :)