Minior

Minior, The Meteor Pokémon. It eats dust in the atmosphere. The composition of the dust determines the color of its core. If its core stays exposed, it will soon die off. It’s possible that it may survive if it’s put into a Poké Ball quickly enough. Places where Minior fall from the night sky are few and far between, with Alola being one of the precious few. It lives in the ozone layer, where it becomes food for stronger Pokémon. When it tries to run away, it falls to the ground. Although its outer shell is uncommonly durable, the shock of falling to the ground smashes the shell to smithereens.

Overview

With access to Shell Smash and a unique ability with Shields Down, Minior is a terrifying late game cleaner in the lower tiers. This in combination with Minior's decent stats for a lower level sweeper are really helpful for this goal. However, its typing is a touch of a let down. While Rock is to be expected, Flying typing is a bit of a hindrance as it makes Minior weak to Stealth Rock as well as limits its resistances, having resistance to only Normal, Poison, Bug, and Flying with a Ground immunity. Not many of these types are really common and a weakness to Water, Steel, Electric, and Rock all hurt, while taking neutral damage from Grass-type attacks is also a problem. Despite these issue Minior is still a powerhouse in lower tier formats and something that must be considered when teambuilding.
Positives
Moves - Minior has access to some nice moves, but not a lot of them. Acrobatics pairs amazingly with Shell Smash as White Herb will negate the drawback of Shell Smash while freeing up the held item spot for the bonus to Acrobatics. Stone Edge and Earthquake also give great neutral coverage so Minior is rarely held back in the moves department.
Speed - Minior is fast, base 120 Speed not only makes it one of the few fast Pokemon in Alola, but also a very fast Pokemon in general. This makes it easy for Minior to take natures that boost its offense since Shell Smash already boosts its Speed to massive levels. Note that Minior is only base 60 Speed in its Shield forme though.

Negatives
One Trick - Minior is a make or break Pokemon that has one chance to pop off or its dead weight. Because of the nature of Shell Smash and White Herb you only have one chance to get the good boost. This is compounded with Minior's ability meaning it has to be half health to be at full power, so if it gets hit hard coming in or takes too little damage instead, it risks being useless. Substitute can help negate this issue, however, as well as pivot support.
Shaky Stats - While Minior's stat spread isn't necessarily bad it's just short in almost all areas which makes it very reliant on Shell Smash. Base 100 defenses in shield form isn't stellar with base 60 HP, and base 100 offenses are unimpressive without a boost. This makes it's all-or-nothing nature even more risky.

Abilities

Shield Down - When below half health Minior changes to core form, gaining boosted offensive stats while losing defenses. While above half health Minior changes to Meteor form, gaining increased defense but losing offensive stats - Similar ideas have been shown to be great with Aegislash and Zygarde Complete, and Minior isn't too different. However, this ability limits Minior's usefulness compared to the other two as it has to be below half health to really abuse Shell Smash, and it also limits any potential defensive utility because it will go from 100 base defense to 60 when it gets below half health.

Movesets

Shell Smash

-Shell Smash
-Substitute / Stone Edge
-Acrobatics
-Earthquake
Item Attached: White Herb
Ability: Pressure
EVs and Nature:
252 Atk / 4 Def / 252 Spe
Adamant Nature

Shell Smash is one of the best boosting moves in the game and makes Minior such a potent threat. Substitute is a nice option as it takes 2 Substitutes, or one and having switched into Stealth Rock, in order to get the forme change from Shields Down. However, this means forgoing Stone Edge as a STAB option which is nice to hit threats such as Rotom who otherwise dodges Earthquake with Levitate. Acrobatics is the main STAB option, as with Shell Smash using up the White Herb, Acrobtatics gains boosted power turning it into a no drawbacks 110 base power move. Earthquake rounds it out for coverage against Steel and Rock threats that resist Acrobatics. Adamant nature with maximum offensive investment is taken to make Minior as powerful as possible after a Shell Smash. Jolly nature is not recommended because Minior's base Speed is already so overkill with Shell Smash with an Adamant nature that it gains very little from the extra Speed here. Investing in bulk isn't very useful either as Minior is ideally ditching its defensive bulk after changing formes. White Herb, as noted before, synergizes with Shell Smash so that Minior doesn't end up being too frail after a Shell Smash and just die to a single hit.

Other Options

Mixed Sweeper - While less ideal, Minior has a decent pool of special attacks it can utilize to try and lure physical walls expecting Minior to be a fully physical set. Power Gem is the only STAB option here so a full special set is not recommended, but Hidden Powers such as Grass or Fire can be used to snipe specific threats such as Rhyperior or Ferrothorn. Psychic can also be used to lure something like Weezing, but there's not a whole lot else it can really hit.
Berries - Other single-use items such as Berries can be used to either boost more or increase longevity while keep Acrobatics utility intact. Liechi Berry stands out in combination with Substitute which can be spammed until you hit the threshold for Liechi Berry to get another boost in damage. Salac also can work but not much outspeeds Minior after Shell Smash and Shields Down's forme change.

Possible Partners

Mow Rotom - Mow Rotom is a great option with Minior as it stomps the bulky Waters that will wall Minior while providing Volt Switch and Defog support. Mow Rotom can also chip at Steel threats and with Hidden Power Fire which beats Excaviler, but the Volt Switch and Defog are the main draws of Mow Rotom.
Toxicroak - Similar to Mow Rotom, Toxicroak can beat most bulky Waters as it can negate their STAB, and is immune to Toxic. Toxicroak can also apply pressure to Steel-type threats that can give Minior a problem if not broken or worn down by the time it hits the field.

Countering Minior

Bulky Water-types - Taking neutral damage from all of Minior's options, except Mantine in the case of Stone Edge, Bulky Waters are the biggest issue for Minior to handle. Milotic just laughs off most attempts to get past it with Scald and Recover. Slowbro can boost up Calm Mind and try to counter sweep if Minior tries to go too early. Mantine can attempt to wall but if Minior has Stone Edge it beats Mantine with Stealth Rock up.
Steel types - Similar to the bulky Waters, Steels are often too bulky for Minior to OHKO without support. Doublade is probably the best with its access to Eviolite and Shadow Sneak to just wall and counter with priority. Registeel is also is just really bulky and can KO with Iron Head. Finally, Escavalier takes neutral damage from Earthquake, but is also neutral to Acrobatics, so it can sponge a hit or two in a pinch.

Locations in Games

Red/Blue/Yellow:
Not in game.

Gold/Silver/Crystal:
Not in game.

Ruby/Sapphire/Emerald:
Not in game.

FireRed/LeafGreen:
Not in game

Colosseum/XD:
Not in game.

Diamond/Pearl/Platinum:
Not in game.

HeartGold/SoulSilver:
Not in game.

Black/White:
Not in game.

Black 2/White 2:
Not in game.

X/Y:
Not in game.

Omega Ruby/Alpha Sapphire:
Not in game.

Sun/Moon:
Mount Hokulani.

Ultra Sun/Ultra Moon:

Let's Go, Pikachu!/Let's Go, Eevee!:
Not in game.

Animé Appearences

Minior has made an appearance in the anime. In its appearance, a group of Minior crashlanded in Alola and then passed.

# -English Episode Name- -Jap. Episode Name- Pics
1022 Showering the World With Love! Minior and Poipole: A Promise that Got Lost in the Starry Skies! Pics
1027 The Shape of Love to Come! The Shape of Family: Poipole's Feelings! Pics
1033 Securing the Future! Connect to the Future! The Legend of the Blinding One!! Pics