Little Tommy Newcomer (Lil' Oondasta) Pet Battle FAQ and Strategy

In patch 5.4 you will find Little Tommy Newcomer on the Timeless Isle. He is located at The Celestial Court right next to Master Li. He offers a daily quest where you have to beat his Lil' Oondasta in pet battles in exchange for 500 Timeless Coins.
The pet hits crazy hard, however the fight is relatively simple with the right team.

Opponent Team

Lil' Oondasta 
Spiritfire Beam - strong vs Flying weak vs Mechanical - Damage ability, hits backline pets as well.

Frill Blast - strong vs Flying weak vs Mechanical - Damage ability, swaps in highest HP pet.
Crush - strong vs Dragonkin weak vs Beasts - Damage ability

Your Team

Wild Jade Hatchling
Tail Sweep, Call Lightning, Lift-Off
Clockwork Gnome 
Metal Fist, Repair, Turret
Clockwork Rocket Bot 
Batter, Toxic Smoke, Launch Rocket

Strategy 

Start with the Wild Jade Hatchling and use Call Lightning to change the weather into Lightning Storm. Lil' Oondasta will likely use Frill Blast here and your Rocket Bot will be swapped in. Use Batter until your bot dies. If your Wild Jade Hatchling survived the Frill Blast it has likely gotten killed by the Spiritfire Beam so use your Clockwork Gnome to finish off Oondasta. Start off with a Turret and then spam Metal Fist until you win. 

If you are unlucky you may have to redo the fight, but so far I have found that this strategy is a fairly easy way to beat Little Tommy Newcomer. 
A video will be up soon showing the fight (I accidentally handed it in today before recording. Duh! ;) )