So, right now, in the 4.3 PTR, the pet from Hallow's End "Sinister Squashling" is BOE. That's right... currenty it is BOP in the game, but come next patch, the item becomes BOE. Of course, since Hallow's End is ending in just a few days, it will be long over by the time 4.3 arrives, so this seems like it wouldn't apply right? Well, it's simple, if you have already earned the item, you can still have one in your bags, either from HH loot-filled pumpkin, or from buying with the treats. So, if you have a lot of alts, you can easily collect at least 1 sinister squashling on each alt, let it sit in your bags in 4.3, and BAM, you will be the only one selling these pets.
This could possibly make you some solid cash as it is likely VERY few if at all on your server will have any of these pets at all until the next hallow's end. And, with the new in-game pokemon battles of Mists of Panderia, this could be a great sell to an impatient collector.
IMO, save some, hold on to them. Maybe you could put 1 up in the AH at a high price just in-case someone is willing to buy.
Anyway, the fortunate thing about this is there is NO COST TO YOU other than the time to get the pets, or the random loot, so if Blizz changes their mind and makes it BOP again, at least you tried. That is unlike the once BOE pet from ZG that blizz was going to get rid of and many of us all bought up like crazy and then last minute blizz adds it back into the game and we all lost some cash haha.
Anyway, good luck, and let's hope these stay BOE. I already have the pet sitting on 4 toons.