Periodic Destruction

So, how this achievement works - At the Laboratory of Mardivas, there is a weekly quest (The Laboratory of Mardivas) where you can summon an elemental and defeat it. Sometimes mobs in Nazjatar can drop Arcane Reagents that can be used at the laboratory to create different creatures: [item=169333] (which I will be referring to as Fire), [item=169332] (Water) and [item=169334] (Sand). Benthic items with the [spell=302381] effect grant an increased chance of looting these reagents from Nazjatar mobs.

There are 6 crystals where you can input reagents on, 3 greater crystals and 3 smaller crystals, and for each creation, you can add a reagent to either 1 smaller crystal, or 1 smaller and 1 greater crystal. After inputting any combination you'd like (or none at all), you create the elemental by confirming your choice in the Essence Amalgamator next to the crystal clusters.

This achievement requires you to invoke and defeat every single combination of elementals that can be created in the laboratory. You can only summon an elemental once a week yourself (if you die, the elemental despawns, but you can simply re-create the creature in the essence amalgamator, not losing your reagents in the process). As you get phased out of groups when on this quest, this will require 13 weeks of summons.

No reagent = Arcane Amalgamation
Small Water = Watery Amalgamation
Small Fire = Burning Amalgamation
Small Sand = Dusty Amalgamation
Small Sand, Great Sand = Herald of Salgos
Small Sand, Great Water = Spawn of Salgos
Small Sand, Great Fire = Salgos the Eternal
Small Water, Great Water = Osgen
Small Water, Great Sand = Zomera
Small Water, Great Fire = Omus
Small Fire, Great Fire = Ungormath
Small Fire, Great Water = Xue
Small Fire, Great Sand = Moghiea

This achievement is a part of the meta Undersea Usurper. You use need the below items in conjunction with crystals to spawn the below mobs using the following combinations.

Coordinates to the cave are: /way Nazjatar 60.31 30.52 Mardivas's Laboratory

The mobs for The Laboratory of Mardivas seem to drop ~2-3 [currency=1721] and the final quest turn in giving 5 [currency=1721]. If you are unsure if you have done it this week you can copy and paste this into your chat log. If "true" is returned it has been completed. If it states "false" then the quest hasn't been done. /script print(IsQuestFlaggedCompleted(55121))

[npc=154970] and [npc=154979] requires [item=169332] each.
[npc=155009] and [npc=155031] requires [item=169334] each.
[npc=154991] and [npc=155025] requires [item=169333] each.

Lesser Arcanocrystal

Greater Arcanocrystal

Spawn

None

None

[npc=155139]

[npc=154970]

None

[npc=150846]

[npc=154970]

[npc=154979]

[npc=150856]

[npc=154970]

[npc=155031]

[npc=150848]

[npc=154970]

[npc=155025]

[npc=151157]

[npc=155009]

None

[npc=150862]

[npc=155009]

[npc=154979]

[npc=150863]

[npc=155009]

[npc=155031]

[npc=150864]

[npc=155009]

[npc=155025]

[npc=151154]

[npc=154991]

None

[npc=150926]

[npc=154991]

[npc=154979]

[npc=150927]

[npc=154991]

[npc=155031]

[npc=150928]

[npc=154991]

[npc=155025]

[npc=151155]

Combining pauladin's table with reidsb's loot list from other pages:

Lesser | Greater

(none)

... Benthic / Water
[item=169332]

... Pyroclasmic / Fire
[item=169333]

... Lithic / Sand
[item=169334]

(none)

[npc=155139]
[item=170477]
[item=170068]

n/a

n/a

n/a

benthic / water ...
[item=169332]

[npc=150846]
[item=170138]

[npc=150856]
[item=170130]

[npc=151157]
[item=170132]
[item=170166]

[npc=150848]
[item=170137]

pyroclasmic / fire ...
[item=169333]

[npc=150926]
[item=170126]

[npc=150927]
[item=170127]
[item=170166]

[npc=151155]
[item=170131]

[npc=150928]
[item=170128]

lithic / sand ...
[item=169334]

[npc=150862]
[item=170383]

[npc=150863]
[item=170124]

[npc=151154]
[item=170129]

[npc=150864]
[item=170125]