XY Ubers First Ubers Team

[Noxiate]

Kyogre @ Choice Specs
Ability: Drizzle
EVs: 4 HP / 252 SpA / 252 Spe
Modest Nature
- Thunder
- Hydro Pump
- Ice Beam
- Water Spout

Kyogre will be my lead for most of the battles unless if i have a better lead vs the opposing team, a Modest, Choice Specs, Max SpA can OHKO most leads with a Water Spout or Hydro Pump with Rain. Thunder and Ice Beam for coverage. Kyogre is considerably bulky and has a high SpA and with Choice Specs, it is a beast lead.

Yveltal @ Leftovers
Ability: Dark Aura
EVs: 252 HP / 4 Atk / 252 SpD
Careful Nature
- Oblivion Wing
- Foul Play
- Toxic
- Roost

My Special Defense Wall for Mega Gengar and Mega Mewtwo and other SpA Threats. Foul Play to kill pokemon that was able to setup vs my team, Toxic and Roost for Stall. Oblivion Wing for STAB.

Groudon @ Leftovers
Ability: Drought
EVs: 252 HP / 228 Def / 28 Spe
Impish Nature
- Stealth Rock
- Earthquake
- Protect
- Toxic

My Physical Defense wall and Rock Settler, Able to Wall out most Physical Attackers and stall with Protect + Toxic. I run 28 Spe so i can outspeed defense Speed ties. Groudon would also Help with changing the weather for fire moves for My Palkia to OHKO Aegislash in Defense form. Earthquake for STAB and because i needed a ground move. Protect because it has helped me win many games in the pass.

Lucario-Mega @ Lucarionite
Ability: Adaptability
EVs: 4 HP / 252 Atk / 252 Spe
Adamant Nature
- Swords Dance
- Bullet Punch
- Close Combat
- ExtremeSpeed

My Physical Sweeper, able to revenge kill most pokemons with Extremespeed and bullet punch, Swords dance if i can set up and sweep. Able to kill Xerneas with +2 Bullet Punch. Close Combat for STAB.

Klefki @ Leftovers
Ability: Prankster
EVs: 248 HP / 252 SpD / 8 Spe
Careful Nature
- Toxic
- Thunder Wave
- Spikes
- Play Rough

My Geomancer Xerneas Wall and crippler with Double Statuses and Play Rough. Able to cripple most sweepers with TWave and most Walls with Toxic. Spikes if i can set up a layer and Play Rough to Kill Dragons and Crippled Xerneas.

Palkia @ Life Orb
Ability: Pressure
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature
- Thunderbolt
- Draco Meteor
- Ice Beam
- Fire Blast

My Special Attacker with Life Orb, Thunderbolt for pokemon's that are able to outspeed my kyogre and kill it. Draco Meteor for STAB, and Ice Beam for Coverage. Fire Blast because i needed a fire move for coverage.

I peaked at 1450~ with this team, Criticism welcome. If you recommend a pokemon for my team in place of another one that is already on my team, feel free to explain why and ill see if i can add it. I want to replace Yveltal with a different Special Defensive wall but i do not know which wall i should use.

 

[Lemonade]

I'm not really great at teambuilding so I won't switch around your mons or anything, but I do have some suggestions set-wise.

I will admit I haven't used Yveltal very much, but I don't think SpDef is very good. First of all, Foul Play uses the opponent's Attack, which means you want to be able to sponge physical hits well, which SpDef does not do. In particular (note you should use 248 HP so you can switch into Stealth Rock one extra time),

+2 252 Atk Silk Scarf Arceus Extreme Speed vs. 248 HP / 0 Def Yveltal: 309-364 (67.9 - 80%) -- 43.8% chance to OHKO after Stealth Rock

This is much shakier of a check than max defense (max damage in that case is 57%). Also, Adamant Ekiller does 74.5% min. But, IMO one of the draws to Defensive Yveltal is the ability to check EKiller (see calc below), which your Spdef set does not do.

+2 0 Atk Dark Aura Yveltal Foul Play vs. 0 HP / 4 Def Arceus: 366-432 (96 - 113.3%) -- 75% chance to OHKO

Furthermore, you don't lose a lot from switching to the Defensive set. Mega Mewtwo-Y can't OHKO with Ice Beam no matter the spread, while Foul Play KOes back. Gengar also does similarly against your SpDef set (Sludge Wave can't 2HKO at full HP and you can't switch into Gengar anyway).

Also for Palkia, Lustrous Orb is generally better than Life Orb because it provides comparable power without the recoil (recoil makes it harder to check stuff like Kyogre):

252 SpA Palkia Fire Blast vs. 252 HP / 252+ SpD Ferrothorn: 348-412 (98.8 - 117%) -- 93.8% chance to OHKO
252 SpA Life Orb Palkia Fire Blast vs. 252 HP / 252+ SpD Ferrothorn: 452-536 (128.4 - 152.2%) -- guaranteed OHKO

Thunder is better than Thunderbolt, especially because against Kyogre Thunder has perfect accuracy anyway, and Rain is up a lot in Ubers. You also want Water STAB like Hydro Pump, over Ice Beam. Neutral Hydro Pump (not in rain) is stronger than a 2x SE Ice Beam anyway with Lustrous Orb, and common Pokemon 4x weak to Ice Beam are OHKOed by your Dragon STAB anyway. I also don't agree with Draco Meteor on a general Special Attacker because with good coverage you don't want that -2 SpA drop. Spacial Rend is the replacement IMO.

I also don't encounter Gothitelle much on the ladder, but if it's giving you trouble you can use Heal Block over Toxic on Klefki to prevent Gothitelle from setting up 6 Calm Minds with Rest and doing a lot of damage to your team (though you do have Yveltal to deal with mono Psychic).

Something to consider is adding a Scarf mon to act as a revenge killer, because your fastest mon is Palkia at base 100. Klefki T-wave works as a soft check to fast threats, but without reliable recovery it can't take a beating. Lucario's Espeed and Bullet Punch are strong, but generally not enough.

 

[Noxiate]

I'm not really great at teambuilding so I won't switch around your mons or anything, but I do have some suggestions set-wise.

I will admit I haven't used Yveltal very much, but I don't think SpDef is very good. First of all, Foul Play uses the opponent's Attack, which means you want to be able to sponge physical hits well, which SpDef does not do. In particular (note you should use 248 HP so you can switch into Stealth Rock one extra time),

+2 252 Atk Silk Scarf Arceus Extreme Speed vs. 248 HP / 0 Def Yveltal: 309-364 (67.9 - 80%) -- 43.8% chance to OHKO after Stealth Rock

This is much shakier of a check than max defense (max damage in that case is 57%). Also, Adamant Ekiller does 74.5% min. But, IMO one of the draws to Defensive Yveltal is the ability to check EKiller (see calc below), which your Spdef set does not do.

+2 0 Atk Dark Aura Yveltal Foul Play vs. 0 HP / 4 Def Arceus: 366-432 (96 - 113.3%) -- 75% chance to OHKO

Furthermore, you don't lose a lot from switching to the Defensive set. Mega Mewtwo-Y can't OHKO with Ice Beam no matter the spread, while Foul Play KOes back. Gengar also does similarly against your SpDef set (Sludge Wave can't 2HKO at full HP and you can't switch into Gengar anyway).

Also for Palkia, Lustrous Orb is generally better than Life Orb because it provides comparable power without the recoil (recoil makes it harder to check stuff like Kyogre):

252 SpA Palkia Fire Blast vs. 252 HP / 252+ SpD Ferrothorn: 348-412 (98.8 - 117%) -- 93.8% chance to OHKO
252 SpA Life Orb Palkia Fire Blast vs. 252 HP / 252+ SpD Ferrothorn: 452-536 (128.4 - 152.2%) -- guaranteed OHKO

Thunder is better than Thunderbolt, especially because against Kyogre Thunder has perfect accuracy anyway, and Rain is up a lot in Ubers. You also want Water STAB like Hydro Pump, over Ice Beam. Neutral Hydro Pump (not in rain) is stronger than a 2x SE Ice Beam anyway with Lustrous Orb, and common Pokemon 4x weak to Ice Beam are OHKOed by your Dragon STAB anyway. I also don't agree with Draco Meteor on a general Special Attacker because with good coverage you don't want that -2 SpA drop. Spacial Rend is the replacement IMO.

I also don't encounter Gothitelle much on the ladder, but if it's giving you trouble you can use Heal Block over Toxic on Klefki to prevent Gothitelle from setting up 6 Calm Minds with Rest and doing a lot of damage to your team (though you do have Yveltal to deal with mono Psychic).

Something to consider is adding a Scarf mon to act as a revenge killer, because your fastest mon is Palkia at base 100. Klefki T-wave works as a soft check to fast threats, but without reliable recovery it can't take a beating. Lucario's Espeed and Bullet Punch are strong, but generally not enough.

If i were to put a choice scarf on my team, who should i replace?

 

[8-BIT Luster]

Hmm...
Put at least three lines of description for each mon, I don't want this to get locked.
On Lucario, I run Rock Slide over ExtremeSpeed because that lets you beat out the king burd Ho-Oh.
On the subject of Luke, Swords dance really functions best in Sticky Web, so I recommend an all-out attacker with Bullet Punch/Iron Tail/Rock Slide or Stone Edge/Close Combat.
Iron Tail may seem like crap on Lucario, but trust me, this thing's the only thing Iron Tail IS good on. Lets you punish Xerneas assuming it hits.

Echoing VOx on the lustKia over LOKia suggestion. Life Orb is pretty meh on Palkia, as lustrous orb is much better, as you really only use Fire Blast for Groudon or steels. I'd also nix Ice Beam, as it provides no special coverage, and replace it with either Thunder Wave or Thunder. TWave lets you cripple Xerneas before dying, and Thunder lets you smack around Kyogre and yveltal.