Hey there! From what I can tell, the goal of your team is to sweep with a Geomancy boosted Xerneas. Unfortunately, a majority of your pokemon aren't viable in Ubers so I can't give you a full rate, but I will give you something to work with to make your team viable.
First of all, change Mega Charizard Y to Primal Groudon.
Groudon @ Red Orb
Ability: Drought
EVs: 252 HP / 56 Def / 200 SpD
Relaxed Nature
- Stealth Rock
- Precipice Blades
- Lava Plume
- Roar
Mega Charizard Y isn't good in Ubers, while Primal Groudon is a top tier pokemon. Primal Groudon fits well alongside Xerneas since it's able to take care of many of Xerneas' checks such as steel types and Blissey.
I've been thinking of replacing something with Arceus-Water to handle opposing Primal-Groudon and Ho-Oh among other things. Arceus-Water also gives you a defogger to remove opposing hazards.
Arceus-Water @ Splash Plate
Ability: Multitype
EVs: 252 HP / 200 Def / 56 Spe
Bold Nature
- Recover
- Toxic
- Defog
- Judgment
As for the rest of the team, Ferrothorn's the only pokemon I would keep. Ferrothorn can help against pokemon like Primal Kyogre so it fits on this team. Jirachi isn't bad in Ubers, but with Ferrothorn already on the team, Jirachi doesn't really do anything that another pokemon can't, in my opinion. For ideas on replacing the remaining two pokemon, keep in mind that the four pokemon I've suggested as replacements or ones to keep are all 2HKOed by offensive Dialga's coverage moves. The team also looks like it gets stopped by Deoxys-Attack if it gets a chance to revenge kill something. Finally, the team doesn't have anything to break past Lugia. Ferrothorn can take on Lugia, but aside from Stealth Rock damage, nothing can deal enough damage to Lugia to net anything higher than a 3HKO. Your best bet with dealing with it so far is to pull off a Geomancy on Xerneas before Lugia can come in and Whirlwind and beat it with Thunder (which I plan to change Dazzling Gleam with since you don't need two Fairy type moves).
The last things to change are the sets for Xerneas and Ferrothorn. For Xerneas, I suggest this EV spread and moveset.
Xerneas @ Power Herb
Ability: Fairy Aura
EVs: 184 HP / 28 Def / 252 SpA / 44 Spe
Modest Nature
- Geomancy
- Moonblast
- Thunder
- Focus Blast
These EVs allow Xerneas to be faster than Choice Scarf Genesect after a Geomancy boost and survive a +2 Normal Arceus' Extreme Speed. Hidden Power Ground wasn't necessary since the addition of Arceus-Water takes care of opposing Primal-Groudon. Thunder is a great coverage move against Ho-Oh and Primal Kyogre. Focus Blast can damage opposing steel types if you predict a switch-in, or if they're weak enough after a Geomancy boost to be taken out by it.
For Ferrothorn, it should be specially defensive with the following set:
Ferrothorn @ Leftovers
Ability: Iron Barbs
EVs: 252 HP / 4 Atk / 252 SpD
Sassy Nature
- Spikes
- Gyro Ball
- Leech Seed
- Protect
Focus Sash is not a good item on Ferrothorn since it's not used as some kind of suicide lead. Ferrothorn is meant to be a defensive check to many pokemon as well as a hazard setter alongside Primal Groudon, so it should never be kept in against pokemon that can OHKO it. Leftovers with Leech Seed can help it recover HP. Protect can help with the Leftovers + Leech Seed recovery as well as scout for a Choice item or moveset.
Finally, I suggest looking at the Uber viability ranking on Smogon to get an idea of what pokemon are good in Ubers at this time. This will help you with finding a good pokemon to fit for your last two slots, since you can run a number of things based on what you want to check/counter and what other things you want to add to the team, for example a Mega pokemon since now you don't have one.
Good luck with the rest of the team!
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