Some of the Pets available in World of Warcraft Classic can be sold for quite a hefty sum of money on the in-game Auction House. Using Pets for yourself is also quite a nice and elegant way to distinguish yourself from the masses. And we all know cosmetic items gradually become more and more important for players but it didn't exactly work like that in Vanilla WoW. There were no transmogs, and the number of Pets and Mounts available was greatly limited. Even though players didn't pay that much attention to visual aspects back then, prices on the rarest Pets could reach astounding levels. If you are feeling lucky enough, you can also make farming Pets a great way to earn money for your first Mount.
Below you will find a list of the Pets which can be farmed in WoW Classic (and doing it can be potentially profitable for you). There are just a couple of Pets/Companions which are lootable from regular monsters, so it's definitely worth knowing where and how to obtain them.
Name: Hyacinth Macaw
Looted from: Bloodsail Pirates in Stranglethorn Vale
Overview: Hyacinth Macaw is the rarest and the most expensive Pet/Companion in WoW Classic. It has a drop rate of around 0,01% - you need to kill between 10,000 - 13,000 Bloodsail Pirates in the Stranglethorn Vale Area, though there have been rumors that it could drop from ANY monster in STV. Hyacinth Macaw's Parrot Cage has been quite a popular item to farm for, since it basically covers up all the Epic Mount expenses - yet finding one is a real challenge.
Name: Disgusting Oozeling
Looted from: Oozing Bag
Overview: Disgusting Oozeling is one of the coolest looking Companion in World of Warcraft Classic. It makes you glow green when you have it active. It has a low chance (approximately 1%) to be found in Oozing Bag that can be looted from various Oozes, Slimes, and Sludges in Felwood, Un'Goro Crater, and Western and Eastern Plaguelands.
Tiny Emerald Whelpling
Name: Tiny Emerald Whelpling
Looted from: Dreaming Whelps
Overview: Tiny Emerald Whelpling is the rarest and the most expensive Whelpling Companion which can be farmed in WoW Classic. It drops only from Dreaming Whelps in the western part of Swap of Sorrows. It's a very common farming spot, so just make sure you aren't wasting time sharing it with a bunch of other players who reduce your efficiency
Tiny Crimson Whelpling
Name: Tiny Crimson Whelpling
Looted from: Red/Crimson Whelps
Overview: Crimson Whelpling, with its drop chance of 0,15% is quite common, but still, it should be worth around 100 Gold on average depending on your server. It drops from any Red and Crimson Whelp in the north-eastern part of Wetlands. It's also one of the first Pets from the list that you can find, with monsters level as low as 23-27.
Name: Dark Whelpling
Looted from: Searing and Scalding Whelp
Overview: Dark Whelping can drop from dragonkin in the southern part of Dustwallow Marsh and the eastern part of Badlands. Both areas have level 40 and above monsters. Dark Whelpling has around 0,1% drop chance, so with quite low price you shouldn't treat it as the most efficient Gold farming method