For this achievement you need to kill 4 bosses in Ahn'kahet: The Old Kingdom, explanations below.

Elder Nadox

1. During the fight he will summon Ahn'kahet Swarmers. Low health and can be killed very fast.
2. He also summons Ahn'kahar Guardian's. At this point everyone in the party needs to DPS them down because they make every other mob in the room immune to damage.
3. Only other noteable thing he does is Blood Plague - damage over time disease which can be cleansed or removed by a priest.

Prince Taldaram

1. Prince Taldaram will randomly spawn Conjure Flame Sphere's which which do little damage.
2. Prince Taldaram randomly Vanishes, during this he will walk towards a random party member and cast Embrace of the Vampyr. This drains 1500 health from the member and healing Prince Taldaram for the same amount. AoE damage will break him out of Vanish so try getting him out fast.

Jedoga Shadowseeker

1. This fight is all about coordination. Initiate the fight and wait for Jedoga Shadowseeker to start attacking.
2. The most noteable thing about this fight is when Jedoga Shadowseeker goes into the air and calls forth her most devoted volunteer. Your whole group needs to dps the volunteer down before they reach the magic circle in the center. If they reach this point, Jedoga Shadowseeker will hit 200% harder and probably wipe your party.
3. When Cyclone Strike is cast all melee need to back up, it hits very hard.

Herald Volazj

1. This fight is really fun, the only thing mentioning is that he will cast insanity. During insanity you will have to face your own character, with low health. Kill them down and resume the fight. Remember the healer will heal, so kill them first.