Cresselia @ Psychium Z
EVs: 252 HP / 4 Def / 252 SpA
Cress will set up Trick Room to allow the slower Aegislash and Snorlax to move first. It can use its Z-Move as well, Shattered Psyche.
Aegislash @ Weakness Policy
Ability: Stance Change
EVs: 252 HP / 252 SpA / 4 SpD
*Again, a bit slow, but Cress TR support can help it get fast and attack opponent's quickly. The Weakness Policy allows it to get a boost from common weaknesses such as Fire, Ghost, and Dark.
Snorlax @ Iapapa Berry
EVs: 68 HP / 196 Atk / 244 Def
Although its a rather slow Pokémon, Cress can support it with Trick Room to help it Curse-boost and then launch strong attacks.
Charizard @ Charizardite Y
EVs: 4 Def / 252 SpA / 252 Spe
Insanely powerful. It can OHKO many Pokémon. It's main threat is Rock Slide, which can be avoided with Wide Guard upport such as Aegislash, although that can be hard to predict. If Tapu Koko or Thundurus are brought into play, it would be good to switch out to Landorus-T because Charizard hates Electric-types.
Tapu Fini @ Choice Specs
Ability: Misty Surge
EVs: 236 HP / 108 Def / 132 SpA / 28 SpD / 4 Spe
An immunity to status through Misty Terrain makes Tapu Fini an excellent Calm Mind user. The spread survives Landorus-T’s Tectonic Rage, and OHKOes back with +1 Muddy Water, as well as Timid Tapu Koko’s Thunderbolt. Leftovers and Sitrus Berry are viable alternative items, although rarely heal as much as a 50% Berry does over the course of a battle. Intimidate users such as Mega Salamence and Landorus-T make excellent partners, as they can reduce the damage Tapu Fini receives from physical attackers. The aforementioned Pokemon are also useful in order to check Grass- and Electric-types, respectively, with their STAB moves.
Landorus-T @ Assault Vest
EVs: 252 HP / 240 Def / 16 Spe
This is such a powerful Pokémon. It can help rid common Electric-type threats like Tapu Koko with one Earthquake. U-Turn can allow frailer teammates switch in without taking damage. Stone Edge is an option to make Landorus-T a solid check to Mega Pinsir, prevent Volcarona from setting up a Quiver Dance on it, stop Mantine from coming in freely to remove its Stealth Rock, and counteract Hidden Power Ice Zapdos.
This team is constructed for VGC doubles.