Sandclaw Nestseeker
Source: Quest. Anything can be a nest, if you try hard enough. Aquatic type. Got it after ~756 chests (I didn't count at the begining). Then, I decided : " Since I'm on it I'm going to finish my " And, of course, I got 2 more in the following minute.
The 
Sandclaw Nestseeker is a cageable Battle for Azeroth pet obtained in Nazjatar by using the 
Scrying Stone to reveal hidden chests throughout the zone.
Guide awaiting review
Obtain the Scrying Stone
Acquire the Scrying Stone by completing a quest in Nazjatar that rewards one directly; after that, Scrying Stones will begin dropping from enemies in the zone.
Use Scrying Stone in Nazjatar
Activate the Scrying Stone to gain an extra action button in Nazjatar, then press it to reveal hidden chests nearby — the Sandclaw Nestseeker has a chance to come from these revealed chests, and using the button also has a chance to spawn a Sandcastle which drops a separate pet called Sandkeep.
Equip N'lyeth for Neutral Mobs
Equip 
N'lyeth, Sliver of N'Zoth with Warmode enabled to turn nearly all enemies in Nazjatar — including naga, water elementals, and murlocs — neutral so they will not interrupt your chest looping; avoid this during Call to Arms: Nazjatar weeks when enemy player activity increases.
Use Stirrups for Mounted Looting
Use 
Monel-Hardened Stirrups to loot revealed chests while remaining mounted, though you must still dismount to press the extra action button to reveal each chest.
Tips
This pet is cageable, meaning it can be traded or purchased from other players on the Auction House if you prefer not to farm chests.
Expect a very low drop rate from the revealed chests — recorded attempts range from roughly 734 to over 756 chests opened before obtaining the pet.
