Mechanical Pandaren Dragonling
I always start out with Trunks and put down Moonlight. Depending on the situation, I may either swap to another pet, cast Avalanche, or perhaps if the enemy pet is weak against your main "When Elekks Fly" attack and you will do "strong" damage to them, I may try that move once or twice even though it only has a 50% hit rate.
Xu-Fu's Spirit Claws does a lot of damage for an ability you can use every turn at 494 damage. The negative is that it has an 80% hit rate...with the exception of when Moonlight is up. Guess what? You already cast Moonlight with Trunks, so now you have a 100% hit rate on a high damage attack. Be sure to heal up with his Feed ability when necessary, and sometimes I even like to use it quite early and swap out to the Mechanical Pandaren Dragonling so I can re-heal Xu-Fu again later.
When you use the Mechanical Pandaren Dragonling, be sure to cast Thunderbolt. It does damage to the entire team, split 3 ways. The key here is that that 592 damage and also even Trunks' Avalanche ability (at a massive 716 damage) are still damage you will need to do to the enemy pets, regardless, so it doesn't matter that you aren't directly attacking their front pet that is in play.
Think of the entire team's health pool as a single number and you will realize how strong those abilities are. They also make great finishers when they only have one pet left as it does all the damage to their single pet. Lastly, they are also useful to kill off pets that are low HP that the enemy may have swapped out to keep it alive...just check their HP that they have left and do the math to see if your Avalanche or Thunderbolt would be able to kill the low health back pet or not.
If you want to swap back to Trunks or Xu-Fu after using the Mechanical Dragonling for a bit, put down a decoy first so you won't take damage during the swap.
This was so successful for me that after playing it for 3 days straight, I randomly am matched up with a player who copied my team, literally pet for pet, lol. That was flattering and quite funny. I'm sure that the Pandaren Dragon can probably be swapped out for something else at your choosing, by the way, but that's just my personal choice as it is an amazing pet. The drop decoy and swap to another pet is a great tactic that I love using with it.