I wanted to wait for my Gen 6 to have an answer, but I got impatient, plus I still have a comment on it that gave me useful changes, so I'm posting this next starter team.
Primarina @Choice Specs
Ability: Torrent
EVs: HP: 252 / Sp.Atk: 252 / Sp.Def: 4
Modest Nature
-Hydro Pump
-Moonblast
-Psychic
-Ice Beam
Normally Primarina is outclassed by Tapu Fini in Gen 7, but Primarina does have a much higher Sp.Atk than Tapu Fini does, so I went with a Choice Specs set to fully make use of it. Hydro Pump and Moonblast are of course STAB, then I have Psychic for Poison types and Ice Beam for Grass types.
Pelipper @Damp Rock
Ability: Drizzle
EVs: HP: 248 / Def: 252 / Sp.Def: 8
Relaxed Nature
-Scald
-U Turn
-Defog
-Roost
To further help Primarina get KOs, I decided to go with a rain team, and thus, I added Pelipper. Scald is reliable and can get annoying burns, U Turn let's me pivot into my attackers, Defog removes Hazards, and Roost keeps Pelipper alive.
Xurkitree @Choice Scarf
Ability: Beast Boost
EVs: Sp.Atk: 252 / Sp.Def: 4 / Spd: 252
Timid Nature
-Thunder
-Energy Ball
-Hidden Power (Ice)
-Volt Switch
I was looking at OU Electric types to add to the team, but then I noticed Xurkitree. I tested it and it performed well, so I chose it as my Electric attacker of the team. Thunder over Thunderbolt because of rain, Energy Ball and HP Ice handle Ground types, and Volt Switch is to pivot.
Garchomp @Rocky Helmet
Ability: Rough Skin
EVs: HP: 252 / Sp.Def / Spd: 252
Jolly Nature
-Earthquake
-Dragon Tail
-Toxic
-Stealth Rock
Garchomp's place on the team is to punish pivoting and add some Hazards, with Skin and Helmet dealing a nice chunk to U Turn users, and completely stopping Volt Switch. Earthquake is the main damage source, Dragon Tail racks up Rocks damage and stops non Fairy set up sweepers. Rocks are Rocks, and Toxic also helps with set up sweepers.
Jirachi @Leftovers
Ability: Serene Grace
EVs: HP: 248 / Sp.Def: 188 / Spd: 72
Careful Nature
-Wish
-U Turn
-Iron Head
-Protect
With a decent amount of bulky pokemon, Wish Jirachi seemed like a nice slot in to keep them alive. Wish let's me heal any of my pokemon, and U Turn helps me get into them safely. Iron Head can get annoying Flinchs, and Protect let's Jirachi get more Leftovers recovery and heal up from its own Wishes.
Mega Gyarados @Gyaradosite
Ability: Mold Breaker
EVs: Atk: 252 / Sp.Def: 4 / Spd: 252
Jolly Nature
-Waterfall
-Crunch
-Substitute
-Dragon Dance
I was thinking of adding Mega Swampert at first, but when I looked at my team, I decided Mega Gyarados would fit better. Waterfall and Crunch are STAB, Substitute can help Gyarados stay safe while setting up, and Dragon Dance let's Gyarados set up. I am Considering running Earthquake aswell, probably over Crunch or Sub.
Pokepaste: https://pokepast.es/8fbd1641253f9273
