Originally Posted by
Mormolyce
Also, you don't have to capture one - you can use any regular pet as a battle pet (with a very small number of exceptions).
You can also level a level 1 pet really fast by fighting creatures way above its level. Example - put your level 16 and 17 pets in your pet slots along with the level one you want to powerlevel. Then go fight something say, level 15. Hit it once with your level 1 and then swap it out and finish the fight with one or both of your other pets. XP is shared so if you can do it with just one pet it's even better. XP doesn't scale with level so your level 1 will shoot up in level really fast. The only thing to beware of is that your pet doesn't die instantly before getting a tag - there are some abilities like the Darkmoon Zeppelin's Decoy that protect it from damage, or you can just hope you get lucky. Or fight a lower level pet.
Also try to beat the pet battle masters if you can, they give a lot of XP for their level. But can be tricky if you don't have the right pet types.