He'sSss All Mine

Rare spawn [npc=203462] in Zaralek Cavern is listed as the source for 2-3x battle pets:

• [item=205147] (more than likely a [npc=203625] drop with the wrong source listed in the Pet Journal)
• 
  
• [item=205151]
• 
  
• [item=205152]

While the other(s) drop(s) directly, for [item=205151] it looks like you'll need to loot a [item=206021] instead and do Sniffenseek to find something like [item=205346]. They have a chance to contain a basic tablet and several designs.

Combining them and completing the ritual will eventually result in your [npc=204343] battle pet and complete He'sSss All Mine which is part of A Niffen's Best Buddy. Kinda hard to keep track of it, but it feels like you may only be able to get one of the Sniffenseek items needed for the process every week (open your treasures after each run, keeping them unopened resulted in players missing their "weekly" drop!) and the Scale drop is gated behind finishing the Tablet.

Step

Item 1

Item 2

Combining Spell

Result

1

[item=206009]

[item=206010]

[spell=411656]

[item=206014]

2

[item=206014]

[item=206011]

[spell=411662]

[item=206015]

3

[item=206015]

[item=206012]

[spell=411663]

[item=206016]

4

[item=206016]

[item=206013]

[spell=411665]

[item=206017]

Ritual

[item=206017]

[item=206021]

[spell=411706]

[item=205151]

Salverun is not impressed when you form him:

Salverun says: SSsseriously? Out of all the veSsselss you could choosSSse for me, thisSss wasss the beSsst you could offer?

Salverun says: The ouroborosSSs in the cssenter of my desSsign wasSss a sSsymbol, it waSssn't meant to be taken LITERALLY!

Salverun says: SssSsuch little visssion for a sSspell ssso powerful...

He'll get snippy at you in whispers too after summoning him for the first time.

I will say you can get more than one Designs per week -- I got Mind and Soul back to back in the same week.