Trick Room Team

Partial TR team probably makes more sense since some of these Pokemon can function outside of Trick Room. I don't have a specific tier I'm using this team for, but OU would be the closest. I'm building this team on my copy of Moon instead of Showdown, so no legendaries for conveniency with time and whatnot. My plan is to use this team against my irl friends, specifically against my friend whose been playing VGC for a few years. This team isn't perfect, and my choices for my Pokemon aren't final. I'm also thinking about switching out one of my Pokemon for another special attacker because Pory2's pretty much the only special attacker I have currently.

The team:

Toxapex (F) @ Black Sludge
Ability: Regenerator
EVs: 252 HP / 192 Def / 64 SpD
Impish Nature
- Liquidation
- Haze
- Recover
- Toxic

Your standard Toxapex wall set except Liquidation instead of Scald. Toxic has better long term effects than a burn from Scald in the long run. Liquidation provides a bit more strength to get rid of stragglers hanging on to low HP, and Toxapex has a better attack than special attack stat.

Ferrothorn (M) @ Leftovers
Ability: Iron Barbs
EVs: 252 HP / 88 Def / 168 SpD
Impish Nature
- Stealth Rock
- Leech Seed
- Power Whip
- Gyro Ball

Another typical Ferrothorn moveset for support and cover for Toxapex's weaknesses. Not much else to say on it.

Mimikyu (M) @ Ghostium Z
Ability: Disguise
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Play Rough
- Shadow Sneak
- Trick Room
- Taunt

The fastest Pokemon on my team; a back up if Pory2 fails to setup Trick Room. I thought about Shadow Claw instead of Shadow Sneak, but went with Shadow Sneak to outspeed moves like Extreme Speed, Bullet Punch, Aqua Jet, and etc. if HP is low. Taunt helps me Taunt other Taunt-users before they get to prevent me from setting up Trick Room.

Porygon2 @ Eviolite
Ability: Download
EVs: 252 HP / 252 Def / 4 SpA
Bold Nature
- Ice Beam
- Thunderbolt
- Recover
- Trick Room

My main Trick Room setter; has a typical Pory2 TR moveset. I'm not sure about having it as my only special attacker because if it gets poisoned by Toxic and faints after some point, I'm pretty much done for if I'm still going against Pokemon bulky in special defense.

Marowak-Alola (F) @ Thick Club
Ability: Cursed Body
EVs: 252 HP / 252 Atk / 4 SpD
Adamant Nature
- Shadow Bone
- Bonemerang
- Flare Blitz
- Protect

The main reason why I have Marowak-A is because I wanted a counter to my friend's Mega-Scizor. Once I get TR up, and switch to Marowak-A at the right time, I could pretty much sweep a part of my opponent's team until TR ends.

Araquanid (F) @ Assault Vest
Ability: Water Bubble
EVs: 252 HP / 252 Atk / 4 SpD
Brave Nature
- Liquidation
- Leech Life
- Poison Jab
- Protect

Araquanid's there to cover up for Toxapex's and Marowak-A's weakness to Earthquake. Poison Jab helps me with hitting Fairy-Types in addition to Ferrothorn's Gyro Ball.

Considering:

Hariyama @ Flame Orb
Ability: Guts
EVs: 92 HP / 252 Atk / 164 Def
Brave Nature
- Fake Out
- Close Combat
- Knock Off
- Feint

I could use Hariyama instead of Marowak-A because most Earthquake-users are probably going to be part Steel-Type or Rock-Type. Plus, Hariyama isn't weak to Earthquake. The downside is my team would probably get screwed by a Mega-Scizor.

Aegislash @ Leftovers
Ability: Stance Change
EVs: 244 HP / 12 Def / 252 SpA
Quiet Nature
- Shadow Ball
- Shadow Sneak
- King's Shield
- Pursuit / Sacred Sword

Ferrothorn could be replaced by Aegislash. Aegislash is a nice choice for a special attacker, but ultimately, I'll have three Ghost-Types on my team, leaving my team more vulnerable to Dark-Types and other Ghost-Types.

Starmie @ Leftovers
Ability: Natural Cure
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Hydro Pump
- Psyshock
- Recover
- Rapid Spin

Possible stand in for Araquanid in case I'm going against people who happen to have the moves Stealth Rock, Spikes, AND Leech Seed all on their team. Some of my Pokemon aren't bulky enough withstand all three of these moves going on at once. Felt like I needed a rapid spinner or a defogger to get rid of these, but Starmie doesn't fit that well on a TR team.

Scald is still the better move for Toxapex. Yes, the burn clashes with Toxic, but burn still cripples physical attackers. Toxapex is very weak anyway; 63 Attack is still rather weak, with the 53 Special Attack coming in close. Scald's burn chance also deters physical attackers like Zygarde from switching in. Toxapex's main job against physical attackers is to catch a predicted physical attacker on the switch with Scald. If it tries to set up, use Haze to wipe away the boosts; or else spam Scald and fish for a burn, Recovering as needed. Toxic is mainly reserved for bulky walls.

Magearna is a better Trick Room setter than Porygon2 because of its better raw power and defensive typing:
-Trick Room
-Fleur Cannon/Flash Cannon
-Flash Cannon/Thunderbolt
-Focus Blast
Nature: Quiet
EVs: 252 HP/4 Def/252 SAtk
Item: Fairium Z/Steelium Z/Electrium Z

Lightning Rod or Rock Head are the better abilities on Marowak because the former gives it an Electric immunity and the latter lets you spam Flare Blitz without the recoil. I wouldn't consider Hariyama over Marowak, simply because Marowak hits harder with Thick Club and has good utility with Lightning Rod if it has it:
-Flare Blitz/Fire Punch
-Shadow Bone
-Swords Dance/Bonemerang
-Stealth Rock/Will-o-Wisp/Bonemerang
Nature: Brave
EVs: 248 HP/252 Atk/8 Def
Item: Thick Club
Ability: Rock Head/Lightning Rod

You can't rely on Trick Room as your primary strategy; once it wears off or your primary setter has been KOed, your slow attackers will struggle against more offensive teams. You need to pack some faster attackers too. You'll have to put Starmie in to give the team some Speed and Rapid Spin support for Marowak. Examples of other faster attackers are Extrasensory Greninja, Tapu Lele, and Mega Chraizard Y; the former two deal with opposing Toxapex effectively while the latter simply hits really, really, hard:

Greninja:
-Hydro Pump/Ice Beam
-Dark Pulse/Hidden Power (Fire)
-Extrasensory
-Gunk Shot
Nature: Naive
EVs: 4 Atk/252 SAtk/252 Spe
Item: Life Orb
Ability: Protean

or
-Hydro Pump
-Dark Pulse
-Water Shuriken
-Ice Beam/Spikes/U-turn/Extrasensory
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Choice Specs
Ability: Battle Bond

Tapu Lele:
-Psychic
-Moonblast
-Psyshock/Focus Blast
-Hidden Power (Fire)/Focus Blast/Thunderbolt
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Choice Specs/Choice Scarf

or
-Psyshock
-Moonblast
-Focus Blast/Hidden Power (Fire)
-Taunt
Nature: Timid
EVs: 4 Def/252 SAtk/252 Spe
Item: Shed Shell

Charizard Y:
-Fire Blast/Flamethrower
-Solar Beam
-Focus Blast/Hidden Power (Ice)
-Roost
Nature: Timid/Modest
EVs: 4 Def/252 SAtk/252 Spe
Item: Charizardite Y

I'd rather not use Araquanid in OU because outside of Water Bubble-powered Liquidation, its other attacks are weak because 70 Attack is mediocre. If you still want something that resists Ground moves and still takes advantage of Trick Room, use Tapu Bulu. The Grassy Terrain it summons mitigates Marowak's Earthquake weakness, though be aware that it doesn't weaken Thousand Arrows and Bonemerang:
-Wood Hammer
-Horn Leech
-Superpower
-Stone Edge/Zen Headbutt/Megahorn
Nature: Adamant/Brave
EVs: 4 HP/252 Atk/252 Spe (Adamant) or 248 HP/252 Atk/8 Def (Brave)
Item: Choice Band

Ghostium Z makes Mimikyu's Shadow Sneak a 100 base power Never Ending Nightmare and that's nothing compared to a Never Ending Nightmare coming from a Shadow Claw (140 BP). You really need to consider the base power of a Pokemon's moves before giving a Pokemon a Z Crystal, as the base power of the Z move will scale based on the power of the original move. As I gave Magearna the Z Crystal slot, Mimikyu is better with Lum Berry as the item. Also, I don't think a Jolly nature is good for Mimikyu, as this makes it too fast to take advantage of Trick Room itself. A Brave nature with max HP/max Attack would be better, IMO, as Disguise ensures that Mimikyu can set up Trick Room and 96 Speed still isn't the best Speed to be at against offensive teams anyway.

If you're planning on using this team in OU, don't think about using Aegislash because it's an Uber.