Iridescent Ooze

[item=183515] is looted from [object=355886] treasure in Plague Watch area in Maldraxxus. The treasure is located up on dam walls holding the jelly of the Fount of Pestilence, so not a place to simply walk to. When mousovering, there's also a weird open pipe up there that made not much sense until the counterpart was found in a cave beyond [npc=158406]'s platform (it's higlighted like a treasure but not shown on the minimap).

To be able to unlock the chest or use the pipe in the cave you have to be [spell=330092]. To achieve that you'll need to touch the green jelly in that area until you have 10x stacks of [spell=330069]. While stacking up for your transformation you'll suffer increasing nature damage. But there's an easy way to avoid being killed, start eating a food that restores a large amount of health over 20sec i.E. Ethereal Pomegranate, Darkmoon Daggermaw (with defensive cooldown), [item=126936] (later cause it's only 10sec and stacking takes longer), Seraph Tenders or Deep Fried Seraph Tenders (will also heal you over time because you are not in combat in the jelly). When you are transformed go into the cave, click the pipe and find yourself placed on the dam shortly after :-)

If you stack up your [spell=330069] at the big jelly pond surrounding Plague Watch, keep in mind that you'll usually enter [spell=334091] there and be killed really fast when touching the jelly, so make sure to get [spell=338920] from [npc=161841].

TomTom:
/way 59.71 71.18 Mask
/way 62.46 76.58 Cave Entrance
/way 57.66 75.83 Treasure

My alternative way to the treasure:
When I didn't know about the Pipe connection I had to find a different way to get to the treasure. When I was transformed I immediately ran to the wall parting Blighted Scar and Plague Watch, looking at the big color beam from Pool of Mixed Monstrosities, then I was using my [item=122124] and on the highest point of my flight curve I activated a Goblin Glider Kit and carefully landed close to the chest.
I've also seen people using Warlock portals or DHs double jumping but I guess only to realize the chest is locked, no idea if they can make it in time with the slow and no mount restriction while [spell=330092].
Important! You won't be able to get this aura from the jelly in the Fount of Pestilence, instead you'll suffer 1345 Nature damage every 1sec from [spell=330135] in there. So you'll have to reach the Plaguefallen Chest with this aura already active which adds a time limit of 2min to your efforts.

This fella is a different color every time you summon it! I've seen red, blue, and green thus far, not sure if there are more.