Relics of a Fallen Empire

Steps for collecting [item=203736] and [item=203735]:

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2. Be level 70 or higher
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4. Head to Heroic ZG
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6. Once inside, head left across the river
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8. Kill [npc=52053] (Need to kill any 2 bosses to enable [npc=52148])
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10. Kill [npc=52059]
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12. Head to [npc=52148]'s temple and, at ground level, go around the south side to pick up [item=203736] or [item=203735] inside the temple to the right by the gong. One of those two Bijous will be present here, the other will be present here but inside the spirit realm.
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14. On your way up to [npc=52148], kill the 4 giant trolls on the corners of the middle level platform.
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16. Head to to [npc=52148]. I hit him once and he went to 1 health, went immune, and began triggering phase 2 and you are pulled into the spirit realm
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18. Once inside the spirit realm, drop down to pick up whichever Bijou wasn't present outside the spirit realm, from the same place you picked up the first Bijou
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20. Peace out in whichever way you prefer
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Edits: Added killing giant trolls, which bijou is where is somewhat random

With the launch of Patch 10.0.7, the reintroduction of several old crafting recipes removed with the retirement of the original Zul'gurub raid are now once again available. Here's how to obtain them:

Collect [item=203736] and [item=203735] from the [zone=1977] Heroic Dungeon. They're located in the center of the zone, inside the pyramid where you fight [npc=52148].
Rather than take the stairs up to the boss, go around either side to enter the interior of the pyramid.
They're rather easy to miss, lying on the ground by one of the gongs near the southern entrance.
Note that the Shattered Bijou is only available during the second phase of the Jin'do encounter, while inside the spirit realm. It's in the same spot as the Fragmented Bijou.

Combining the two will create [item=203737], which can be turned in to [npc=143138] in Zandalar. Alliance players beware, you'll probably need a quick exit after turning it in.
Turning it in will earn you Relics of a Fallen Empire, which unlocks account wide access to the reintroduced ZG recipes and crafting materials.
A version of Rin'wosho will now be available inside the dungeon by the entrance, selling recipes/ensembles.

Additional Notes:

• Items needed to buy the recipes/ensembles won't drop until after you've finished the achievement.
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• All the items needed to buy the recipes & ensembles can be farmed within the dungeon.
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• All the troll mobs in the dungeon have a low chance of dropping Hakkari Bijou and Coins, even the neutral ones like [npc=52437].
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• All the trolls mobs have a low chance of dropping Massive Mojo
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• Bosses are guaranteed to drop one Hakkari Bijou.
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• Bosses have a low chance of dropping [item=203774], which contains several Hakkari Bijou.
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• Bosses have a low chance of dropping tradable ancient patterns like Ancient Pattern: Gloves of the Tormentor
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• [item=203959] have a low chance of dropping epic ancient patterns like Ancient Plans: Venomreaver
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• Alchemists with 300 skill in Classic Alchemy can interact with the [object=180368] in the Cache of Madness to learn how to craft [item=19931].
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• Skinners can get Primal Tiger Leather and Primal Bat Leather from the Bats/Tigers in the dungeon
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• Fishing can yield caches like [item=203743] and [item=203912], which can contain Hakkari Bijou and Coins, or removed items like [item=19946].
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• You can exchange Coins for [item=203914] from a repeatable quest offered by Rin'wosho inside the dungeon. He'll only offer the quests if you already have the coins needed.
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The boss bugs out unless you kill the giant trolls on the path to him. If you're max level you they'll just ignore you, and without being killed, there's no spirit version of them to kill the chains.