For this exploit you need 2 powerful lvl 25 pets strong enough to kill 3 pets from pet trainer and a little luck for the low lvl companion to survive 1 turn,
1.You add to your team 2 pets strong enough to kill those 3 lvl 25 pets that trainer has
2.You add the low lvl companion as first pet
3.You go at pet trainer,ex Courageous Yon - NPC - World of Warcraft and fight him
4.You use the low lvl companion one turn,atack or pass,if u live change to the oher companions
5.If u win the battle the low lvl gets like 1300xp,normaly gives 287 from a normal pet fight,that's a better way to lvl you pet and faster.