The Twin Guardians (First Named Encounter) in the Palace of the Ancient One Raid Zone. Completing this encounter requires someone in your raid having completed a Heroic Quest Line in the Shadowed Cleft area of Lower Moors.
The Quest is called Frozen out of time and the NPC is called Chipp the Thinker and you can find him around the location of -1451.91, -1013.10, -25.58
The reward is a Void Energized Amulet of Crystallization.
You can not fight these two mobs at the same time, if one is not frozen they will AOE the raid extremely hard. The amulet will freeze one of the mobs for 5 minutes. You have 5 minutes to kill the first named and then move on to the second.
Both of the raid mobs are exactly the same and will put a curse on one person in your raid every minute or so. It will warn you before you get cursed. It will say something to the effect of "You feel a powerful curse being cast upon you" in red letters on your screen (this is incidentally the same message that you will see in the Anashti fight). Five seconds or so after seeing this message you will be cursed. You can not use any abilities while this is on you. If you do, you will bring down a massive AOE called "Negative Flux Storm" which, if you have very little T4 raid gear, will one shot most people in your raid.
The curse is curable so just set up designated curers right away and it shouldnt post much of a problem.
Deal with each named the same way and you should be fine, grats on the easy loot.