Here's an easy way to get the achievements: Win Streak - Achievement - World of Warcraft Legendary Pet Brawler - Achievement - World of Warcraft and Legendary Pet Battler - Achievement - World of Warcraft . You will need a program to constantly press a button every few seconds on both accounts, there are alot of these on the download.com and can be found with a google search as well. And you will also need 2 accounts, one of the accounts needs to have a pet that can preferably one shot your 2nd account's level 1 pet, keep in mind that the low level pet can still sometimes dodge abilities.
IF you have all three roster slots full, fill the first 2 spots with lvl 1 pets and go find a wild matches to kill them, and then win it with your last pet standing. This will let you skip the pet selection process when doing pet pvp battles.
Next, you'll need 2 macros.
Code:
/script C_PetBattles.StartPVPDuel("Target");
On the other account, make the macro
Code:
/click StaticPopup1Button1
.
Next move the macro to the number 1 spot on your toon that is taking the losses, and then move the macro to the 1 shot ability on the toon that is getting the wins.
Lastly, setup your macroing program to spam the appropriate key for the appropriate instance of wow, target the other toon, and go afk for a few hours.
Edited the macro a little.