So here's my entry for the weekly teambuilding competition!
Here's some of my reasoning for the building process:
Origin Story
With the duo of Dondozo and Tatsugiri getting banished to the shadow realm lil' poor Marshadow really lost its most impressive niche as a powerful check able to steal the catfish's omniboost thanks to its signature move Spectral Thief and it's very difficult to justify its presence in a team when a Pokémon like Annihilape exists*. Not only Ape is a little bit bulkier but its access to the incredibly busted Rage Fist crowns the monkey as the better Bulk Up user too. What I wanted to do then was to try playing around with a set and some synergies that make more use of Marshadow's higher speed and access to a boosted priority move in Shadow Sneak.
The Team
To put it very bluntly, the team is conceptualised to be a goodstuff that finds in the combination between solid, bulky but offensive mons and Coaching its main capstone. Vulcanion, Tapu fini and Mega Salamence are good answers to Sun, Zeraora, Rillaboom and Vulcanion are able to cause havoc into Trick Room-based teams, the dual terrain is able to shut down Psyspam and the match up against Rain is generally favorable.
Zeraora
Zeraora is definitely the star of the team: it presents itself as an incredibly fast lead rich in utilty that is also able to preserve its Coaching boosts for later thanks to the wonderful combination of anti-Fake out Cover Cloak and fast Volt Switch. Its ability Volt Absorb synergises quite well with the Electric-weak Tapu Fini and Vulcanion and can be used for interesting mind games.
Tapu Fini
Fini's Ability Misty Surge is quite useful while facing sporers and Will-o-Wispers that can really ruin your opportunity of snowballing while relying on Coaching. The latter move combined with Calm Mind can really create an impressive defensive tank given the circumstances and its typing makes it a natural companion for Marshadow.
Rillaboom
Quite the straightfoward choice: strong fake-outer, incredible Coaching abuser thanks to its two signature stabs, ground resist, my only hope to hit supereffectively Water and Ground types without many logistical issues.
Marshadow
Clearly the Dark horse of the team thanks to its very unique set and item choice: after terastralising against its counters and/or after one Coaching from Zeraora (depending on the circumstances) it's gonna be not only a very fast and strong enough mon able to cripple the other side of the field with a vaste coverage of moves no matter the match up but it will also be quite complicated to K.O., even for its natural counter like Flutter Mane and Tornadus that now cannot stand a 1v1 against it. Its access to Shadow Sneak can also be used effectively as part of a Priority Spam combo with Rillaboom or as a tool to help Salamance, Vulcanion and Tapu at being more technical with the outputs of their spread moves.
Mega Salamence
Salamence, in switch-in and before mega-evolving, is quite useful to reduce the damage of phyisical threats against Marshadow and/or Zeraora and its Tailwing is the main form of Speed control of the team, quite the important condition to let Fini and Volcanion snowball more easily. Even with just one boost of Coaching its Double Edges are gonna 1 to 2hko pretty much everything in sight and Breaking swipe is quite useful as a late game alternative to Intimidate.
Volcanion
Tera Grass Volcanion is quite the strong, one-for-all Trick Room answer and its large coverage of special stabs is exactly what I needed as this team lacks other powerful and immediate special attackers. Heavy Slam can be quite useful against opposite Fairy types, especially in situation when it's not possible to teracristalise Marshadow.
*Team was clearly made before the quickban, please understand >.<