Pelipper @ Damp Rock  
Ability: Drizzle  
EVs: 252 HP / 252 Def / 4 SpD  
Bold Nature  
- Roost  
- Defog  
- Scald  
- U-turn  

Swampert-Mega @ Life Orb  
Ability: Swift Swim  
EVs: 252 Atk / 4 SpD / 252 Spe  
Jolly Nature  
- Waterfall  
- Earthquake  
- Superpower  
- Ice Punch  

Kyogre @ Eject Button  
Ability: Drizzle  
EVs: 144 HP / 252 Def / 112 SpA  
Modest Nature  
IVs: 0 Atk  
- Roar  
- Scald  
- Thunder  
- Icy Wind  

Slowbro-Mega @ Leftovers  
Ability: Shell Armor  
EVs: 252 HP / 16 Def / 240 SpD  
Relaxed Nature  
IVs: 0 Atk / 0 Spe  
- Slack Off  
- Iron Defense  
- Calm Mind  
- Scald  

Dugtrio @ Groundium Z  
Ability: Arena Trap  
EVs: 252 Atk / 4 SpD / 252 Spe  
Adamant Nature  
- Stealth Rock  
- Memento  
- Toxic  
- Earthquake  

Manectric-Mega @ Choice Specs  
Ability: Intimidate  
EVs: 4 Def / 252 SpA / 252 Spe  
Timid Nature  
IVs: 0 Atk  
- Switcheroo  
- Volt Switch  
- Thunder  
- Hidden Power [Ice]  

Team Description:
Threats & Counters: 
S-tier Threat: P-Groudon (specifically double dance) - Counters: Eject button roar Kyogre, Arena Trap Z-Duggy, EQ M-Pert, Intimidate Manectric
S-tier Threat: Jolly Mega-Salamence - Counters: Iron Defense Slowbro, Intimidate HP Ice Manectric
S-Tier Threat: Adamant Mega-Salamence - Counters: Iron Defense Slowbro, Intimidate HP Ice Manectric, Eject button Icy Wind Kyogre
A-Tier Threat: Stall teams - Counters: Toxic Dugtrio, Setup Slowbro, Switcheroo Manectric
A-Tier Threat: Trick room teams - Counters: Setup Slowbro, Switcheroo Manectric, 
(I encounter very little stall and trick room teams on the ladder so I don't have the best answers for them)
The team is played as a mix of Hyper Offense and Bulky setup with a few tech options for big threats. 

1. Pelipper is straight forward. PhysDef with defog and u-turn for momentum into M-Pert or M-Manectric.
2. Mega-Swampert with LO and 4 attacks covers most of the tier and the current meta. No need to worry about intimidate since Salamence and Gyarados start in their mega forms. We run Jolly mostly to out speed and punish Adamant M-Salamence after 1 DD. It is also important to note that we live a Precipice Blades from an Adamant max attack Primal-Groudon after rocks. 
3. Kyogre is modest with a lot of PhysDef and the primal role is to help remove P-Groudon so M-Slowbro can sweep. After initial testing I found that regular eject button Kyogre supports the team much better than Primal-Kyogre. Eject button allows Kyogre to act as a "turn free" rain setter. Kyogre is our primary switch-in for P-Groudon as we easily live any hit with our bulk and get a free switch to Dugtrio to fire off a Tectonic Rage. Roar is used to prevent double dance Primal-Groudon from setting up. The PhysDef IV's allow us to live a +1 Double-Edge from Jolly Mega-Salamence guaranteed, and a chance to live if adamant. Icy Wind is used over ice beam in case M-Mence is running Yache berry and goes for a second DD. Icy wind is more for support and covers a small niche, so feel free to run ice beam over icy wind.  Thunder is mostly used for Mega-Slowbro as it does around 75%. Calm Mind can be run over Roar if you don't find yourself using roar very often. 
4. Mega-Slowbro is our setup sweeper. After rocks damage and with leftovers we can survive a +1 Double-Edge from Jolly M-Mence and click Iron Defense to live the second one and then recover off the damage. If adamant we can still survive from full (no rocks). With P-Groudon gone, this mon can setup and beat any offensive/balance mon in the tier, aside from toxic stalling mons. Slowbro is min speed to help counter against trick room teams. 
5. Dugtrio has one role on the team... Trap and Kill P-Groudon. We run adamant to help guarantee the OHKO with Tectonic Rage. This really is the only role Dugtrio has so we don't care about being Jolly for the extra Speed. Duggy is a good sack after P-Groudon is gone for getting in one of our threats. 
6. Mega-Manectric is another rain abuser with Choice Specs Thunder for huge damage. Volt Switch and HP Ice are pretty standard. We run the tech Switcheroo to help cripple stall and trick room teams. Scarf can be used over specs to help kill Mega-Mence/Mega-Gyarados after 1 DD.