Why is it half of an exploit? Because you are not supposed to heal any damaged pets while in the scenario and out of combat during the scenario. But you are using a pet to heal other pets which is working as intended.
We need a magical crawdad for this to work. Obtainable from fishing in certain fishing pools in terokkar forests if you manage to fish Mr. Pinchy and get the pet from one of the three wishes. Now you need to level the crawdad up to the level to use Wish.
Now for the "we go and heal every pet we need for the next battles - half exploit". While on the tournament, make a team that consists of the crawdad and your damaged pet. I suggest you get an addon that can save pet teams like this one. Now start a battle with Yu'la which wont do any damage in the first two rounds. Yu'la will cast a defensive ability and you cast wish. Switch to your damaged pet. Yu'la will lift off. Watch the damaged pet getting healed up to 50% of its max health. Abort the fight and profit.