Seething Slug

To be able to see the [object=386086] and loot the [item=192779] you'll need to pick up 3x stacks of a [spell=399342] debuff from Seething Orbs located in the Zaqali Caldera area in Zaralek Cavern.

• It looks like players share these orb spawns, but no idea how long it'll take one to respawn when clicked once, it doesn't feel like they are respawning fast.
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• In data, the [spell=399342] aura has the "Leave World Cancels" and "Enter World Cancels" flags which would suggest losing the debuff only on log-in & log-out. But players are reporting they're also losing it while zoning.

Hotfixes May, 4th
Seething Cache now correctly cancels Insidious Insight on all players after being looted by the first player to reach it.

• Honestly, I have no clue how this is supposed to help at all... but maybe it doesn't necessarily mean that players who get theirs removed won't see the Cache anymore.

Players have found more and more locations for these Orbs, so check all the other comments for the mount item. Without them on PTR I personally found it helpful to die and fly around as a spirit to find some. (I don't recommend that for Retail, on populated servers finding an orb and then resurrecting and getting back may take too long while others pick it up and trigger the despawn). For me, the Orbs were located here:

/way #2133 28.75 55.30 [object=386083]
/way #2133 29.95 47.97 [object=401904]
/way #2133 34.41 45.71 [object=401905]
/way #2133 32.33 39.35 Seething Cache

When you get your third stack, you'll see a "You hear a dark hiss from the northern shrine..." system message. So head there, and interact with the now visible [object=386086] to get your Seething Slug.
Looting the Cache flags Hidden Quest [quest=73410] complete for the whole account, so other characters won't see any Orbs.

Orb Locations:

/way #2133 25.24 44.80
/way #2133 26.70 47.00
/way #2133 27.66 49.01
/way #2133 27.95 51.21
/way #2133 28.75 55.30
/way #2133 29.02 41.94
/way #2133 29.15 42.50
/way #2133 29.95 47.97
/way #2133 30.20 40.00
/way #2133 31.18 51.95
/way #2133 32.72 52.23
/way #2133 32.82 52.13
/way #2133 34.41 45.71
/way #2133 35.63 48.77
/way #2133 35.79 41.39
/way #2133 36.20 44.01
/way #2133 37.59 46.72

I was some how able to finally get this mount after less than 3 minutes of searching. I think it was the diablo 4 server slam. My shard is entirely empty and zero rares are being killed.

The jumping sound effects for this mount are juicy.