The Thundering Serpent Hatchling was a real easy pet to get back in Pandaria. You could just buy it off of the guild vendor.
However, they took it out of the game, and now it is impossible to get for anyone who started playing after Panderia.
SOLUTION: Bring the Thundering Serpent Hatchling back, but put it on the Panderia Time Walking vendor. This seems like a really good fit for getting an item from the past, and would allow new players to get the pet.
That’s a good idea. Or simply put it back on the Guild Vendor.
The Deathwatch Hatchling from the WoD guild-achievement was left on the vendor, so I never understood why they had to remove the Thundering Serpent Hatchling.
Side note: The Thundering Serpent Hatchling is supposedly still available in-game. You just need to buy the “right” Unclaimed Black Market Container from the BMAH, and be extremely lucky on the drop from it. Apparently it’s something like 1 in 200 drop chance, but that’s not including the RNG involved in getting the Container.
Its following the same reason they removed the Long Boi mount and put it too the BMAH too keep it rare I guess…I never got it back in MoP I wasn’t big into battle pets back then…I only got into Battle Pets with WoD cause of rip they did to gathering professions like herbs and ores since they put all that into everyone’s Garrison thus killing the AH market for those items…I made great bank on Battle pets from WoD onto beginning of BfA where it fell off.
Unfortunately, no one has ever been able to confirm the Thundering Serpent Hatchling has ever dropped from a BMAH container. Chances are you just can’t get it in-game anymore.
My pet battling skills are terrible. I haven’t won a lvl 25 pet battle yet. I guess I don’t have my battle pets all spec’d out, and trying to line up which Pet I should use to compete with these other pets is beyond my abilities. I rarely do pet battles anymore, and I have hundreds of pets i’ve accumulated over 16yrs. of playing .
Agree they need to bring it back, the inconsitency with pets is really starting to grate on me.
Thundering serpent hatchling = taken out of game for no good reason,
WOD equivalent Deathwatch hatchling= still obtainable
Original CE pets, Diablo CE pets, TBC/wrath/cata CE pets= all unobtainable bar getting an old physical copy with an unused code for thousands $$ off ebay.
MOP CE = randomly brought back to the digital store.
Baby blizzard bear =4th anniversary FOS-unobtainable
Molten Corgi = 10th anniversary FOS- fully purchasable at any time during ANY anniversary event for TW badges. 
Like at this point it is infuriating. Please be consistent blizzard, let ALL anniversary pets be purchasable during the anniversary event with badges- even if that means the older pets cost thousands of TW badges- but at least they are there.
Put the thundering hatchling BACK on the guild vendors.
Put all CE pets on the digital store (wouldn’t blizzard rather profit from this than let other people profit on ebay? Isn’t that what real money traders are doing? Profiting off blizzards intellectual property? See what I mean here, the inconsistency is driving me crazy. )
/ End rant. 