After 20+ hours of desperate attempts and 100+ dead pets I was finally able to complete the Celestial Tournament. This quest is insanely hard but the rewards from it are well worth the effort.
Here is how to beat the 4 Celestial Pets along with Lil' Oondasta. The Celestial Tournament consists of total 7 fights ( 3 legendary pet teams and 4 legendary elite boss solo pets ). The pet tamers are fairly easy so I'm only going to explain the celestial pet fights. The tournament is a solo scenario weekly quest. However, you can fight Lil' Oondasta every day just outside the arena.
Yu'la, Broodling of Yu'lon
Team:
●Dandelion Frolicker
●Dandelion Frolicker
●Bonkers
Explanation:
You need fast pets with strong humanoid attacks. Pets with interrupts ( Kick ) such as Dandelion do very well but mine weren't able to beat her. Her first ability is her shield so make sure you damage her before she puts it up. After that spam your interrupt and dodge abilities as much as possible. She no longer has Life Exchange - She now uses Lift-Off which makes her fairly easy although it does a lot of damage.
Chi-Chi, Hatchling of Chi-Ji
Team:
●Shimmering Wyrmling
●Spectral Porcupette
●Spectral Porcupette
Explanation:
Chi-Chi now starts with Tranquility, followed up by Quills and only after that does she use her Ethereal. I started off by using Feedback followed up by Deflect and afterwards I use my Amplify Magic. After your Wyrmling dies, switch to one of the Porcupettes and time your Spectral Spikes which wins you the fight. Afterwards you just need to spam Powerball while Spectral Spine and Spikes ore on cooldown.
Xu-Fu, Cub of Xuen
Team:
●Darkmoon Zeppelin
●Darkmoon Zeppelin
●Darkmoon Tonk
Explanation:
I used the Darkmoon Zeppelins for 2 specific reasons. Their Explode ability which deals a very nice amount of damage and more importantly their block ability. All you need to do is use Block when Xu-Fu drops to ~70% hp to block his Feed. The rest is just dealing as much damage as possible.
Zao, Calfling of Nuizao
Team:
●Sunreaver Micro-Sentry
●Zandalari Anklerender
●Zandalari Anklerender
Explanation:
Nothing special about this fight. Open with Fel Immolate followed up by Call Lightning. Spam Fel Immolate until your Micro-Sentry dies ( Not more than 1 turn after using Call Lightning ). After that victory becomes simple. Switch to one of the Zandalari Anklerenders, use Black Claw and proceed with Hunting Party which is supposed to end the battle. You won't even need to use your third pet.
Lil' Oondasta
Team:
●Sunreaver Micro-Sentry
●Zandalari Anklerender
●Zandalari Anklerender
Explanation:
This fight is a little bit different than Zao. You open with Call Lightning. Right after that your pet get's switched to one of the Zandalari Anklerenders for free because of Oondasta's ability. Proceed with Black Claw and then Hunting Party. If Oondasta is still alive after that and your raptor dies, just use your second one.
UPDATE: Added Lil' Oondasta fight to the guide and updated the other 4 fights' explanations and team compositions.
I hope this was helpful and wish everyone good luck!