Hello, good team and welcome to Smogon
Uxie @ Gyaradosite
Ability: Levitate
EVs: 252 HP / 252 Def / 4 SpD
Relaxed Nature
IVs: 0 Atk / 0 Spe
- Stealth Rock
- Magic Coat
- Trick Room
- Memento
Since Uxie is a suicide lead, and carries no recovery throughout the match, it will have to accomplish as much as possible as a lead.
Gyaradosite, while saving Uxie from nasty single Psychic-typing, allows Uxie to set Stealth Rock ignoring opposing Sablenite / Absolite users. This way, the only way to stop Uxie from setting Stealth Rock is using Taunt, which can be reflected by using Magic Coat (this should be fairly predictable since the most relevant Taunt user is Deoxys-S).
Trick Room is mandatory for the rest of your team to run rampant for couple turns, and Memento allows your next switch-in to setup on weakened foe or force a switch.
EV's should be used to maximize Uxie's Defense bulk because such spread will let it survive U-turn against Pinsirite Genesect's U-turn which is
x4 effective against Uxie after Mega Evolving with Gyaradosite (Because Uxie will have higher Defense this way, Genesect will gain Sp.Atk from Download prior to Mega Evolution:
252 Atk Pinsirite Genesect U-turn vs. 252 HP / 252+ Def Gyaradosite Uxie: 268-316 (75.7 - 89.2%) -- guaranteed 2HKO
While some people might find this inferior choice of Trick Room lead because of x4 weakness to bug, Uxie's natural bulk combined with Gyaradosite boost lets it live almost any hits. Also, Levitate lets you play around against something like Primal Groudon. I would suggest you to use this as a lead instead.
Sadly, with your current team, someone in your team will have to be sacrified every time Primal Groudon comes out from opposing team. Therefore, here is Golisopod which is still a notable threat outsides Trick Room, one of the best Primal Groudon switch-in's, and runs rampant in Trick Room with its low Speed:
Golisopod @ Blue Orb
Ability: Emergency Exit
EVs: 248 HP / 252 Atk / 4 Def
Brave Nature
IVs: 0 Spe
- Liquidation
- Aqua Jet
- Leech Life
- Swords Dance
With Blue Orb granting it 50 Attack and Primordial Sea upon Primal Reversion, Golisopod hits like a truck even without a boost, and will wrect havoc on teams without Red Orb users. If you can predict a switch, set Swords Dance, and if you are low on health, use Leech Life for some health.
Aqua Jet is still necessary even though Golisopod is meant to be one of the Trick Room sweepers in your team, because it leaves Golisopod with something worthwhile to do (namely revenge killing) when you are not able to set up Trick Room.
About your Magearna, give it Volt Switch so you can bring in your sweeper reliably.
Rhyperior @ Heracronite
Ability: Solid Rock
EVs: 252 HP / 252 Atk / 4 Def
Brave Nature
IVs: 0 Spe
- Earthquake
- Rock Blast
- Ice Punch / Fire Punch / Thunder Punch
- Swords Dance
This seems like a better set to me. Outrage, while OHKOing Zygarde is sweet, may lead to you wasting your Trick Room turns by giving free switchin to fairy. Also, Heracronite provides more attack, lowers your speed so you are even faster in Trick Room, and allows your Rhyperior to use always-5-times-hitting Rock Blast. Swords Dance is there to boost the attack to apocalyptic levels on predicted switch, and you will have a chance to OHKO Sablenite Blissey after Stealth Rock damage. The third move depends on the rest of your team, and I would presonally recommend Ice Punch on top of everything so you can OHKO Zygarde which would otherwise survive a hit. Especially if you are against Pinsirite variants, you may miss your Earthquake as Zygarde gains Flying-type on Mega evo and resist Rock Blast if it decides not to.
I am not the best Mix and Mega player and council team should be able to give you better advice about your team. But it seemed like not many gave attention to your post at this moment so I stopped by. Hope this helps and good luck.