Counter that Pokémon!

Mimikyu @ Life Orb
Ability: Disguise
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Swords Dance
- Shadow Sneak
- Play Rough
- Shadow Claw

3/4 attacks can't touch Mimikyu and disguise absorbs Knock Off (and even if it didn't your ohko isn't guaranteed). Then Mimikyu outspeeds and OHKOs with Play Rough.

(Cloyster) (M) @ Focus Sash
Ability: Skill Link
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Icicle Spear
- Rock Blast
- Shell Smash
- Razor Shell
Hits even with Disguise should counter but only has a 6.3% OKHO chance.

Team Embrace said:

(Cloyster) (M) @ Focus Sash
Ability: Skill Link
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Icicle Spear
- Rock Blast
- Shell Smash
- Razor Shell
Hits even with Disguise should counter but only has a 6.3% OKHO chance.

Click to expand...

I'm not sure whether this should be called out or not. Technically it's not a counter by the definition that was linked in the first post.

It does take a +2 Play Rough in all cases even without the Sash, and has a 93.8% chance to KO after Life Orb recoil. Though if you don't manage to kill, Mimikyu kills you with Shadow Sneak then faints itself due to Life Orb. In that circumstance, you actually lose first because you are the first to faint. I think a more appropriate counter would just be to use something like NeverMeltIce instead of Focus Sash.

Anyway, I guess I'll post this Empoleon set to counter your Cloyster:

Empoleon @ Leftovers
Ability: Torrent
EVs: 252 HP / 4 Def / 252 SpAtk
Modest Nature
- Hydro Pump
- Ice Beam
- Flash Cannon
- HP Electric

Magnezone @ Choice Specs
Ability: Magnet Pull
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature
- Thunderbolt
- Volt Switch
- Flash Cannon
- Hidden Power Fire

Zeraora @ Fightinium Z
Ability: Volt Absorb
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Plasma Fists
- Close Combat
- Knock Off
- Hidden Power [Ice]

Venusaur @ Venusaurite
Ability: Chlorophyll
EVs: 248 HP / 88 Def / 156 SpD / 16 Spe
Calm Nature
- Leech Seed
- Sludge Bomb
- Synthesis
- Hidden Power Fire

Chandelure @ Choice Specs
Ability: Flame Body
EVs: 252 SpA / 4 SpD / 252 Spe
Modest Nature
- Fire Blast
- Shadow Ball
- Energy Ball
- Hidden Power [Fighting]

252+ SpA Choice Specs Chandelure Fire Blast vs. 248 HP / 156+ SpD Thick Fat Venusaur-Mega: 218-260 (60 - 71.6%) -- guaranteed 2HKO

Blissey @ Leftovers
Ability: Natural Cure
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
- Seismic Toss
- Toxic
- Soft-Boiled
- Heal Bell

Gengar @ Life Orb
Ability: Cursed Body
EVs: 252 SpA / 4 SpD / 252 Spe
IVs: 29 HP
Timid Nature
- Shadow Ball
- Sludge Wave
- Taunt
- Focus Blast

Muk-Alola @ Assault Vest
Ability: Poison Touch
EVs: 4 HP / 252 Atk / 252 SpD
Adamant Nature
- Pursuit
- Gunk Shot
- Knock Off
- Fire Punch

Garchomp @ Groundium Z
Ability: Rough Skin
EVs: 4 HP / 252 Atk / 252 Spe
Jolly Nature
- Earthquake
- Swords Dance
- Outrage
- Stealth Rock

Togekiss @ Babiri Berry
Ability: Serene Grace
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Nasty Plot
- Air Slash
- Flamethrower
- Roost

Aerodactyl @ Aerodactylite
Ability: Unnerve
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Stone Edge
- Earthquake
- Aqua Tail
- Pursuit

Swampert@Leftovers
Ability: Torrent
EVs: 252 HP / 252 Def / 4 Spd
Relaxed Nature
-Stealth Rock
-Scald
-Toxic
-Earthquake

Serperior @ Leftovers
Ability: Contrary
EVs: 252 SpA / 252 Spe / 4 Def
Timid Nature
-Leaf Storm
-Hidden Power Fire
-Glare
-Leech Seed

Heatran @ Firium Z
Ability: Flash Fire
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature
- Magma Storm
- Taunt
- Earth Power
- Stealth Rock

Flygon @ Dragonium Z
Ability: Levitate
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Dragon Dance
- Earthquake
- Outrage
- Fire Punch

Empoleon @ Leftovers
Bold Nature
Ability: Torrent
EVs: 252 HP / 252 Def / 4 SpA
- Ice Beam
- Scald
- Defog
- Taunt
This dude can tank an Earthquake, even a critical Earthquake that deals 368 or less, then goes for Ice Beam to OHKO your Flygon.

As long as you choose anything other than Earthquake for the best, you fall to one Ice Beam.

Anvils Alive said:

Empoleon @ Leftovers
Bold Nature
Ability: Torrent
EVs: 252 HP / 252 Def / 4 SpA
- Ice Beam
- Scald
- Defog
- Taunt
This dude can tank an Earthquake, even a critical Earthquake that deals 368 or less, then goes for Ice Beam to OHKO your Flygon.

As long as you choose anything other than Earthquake for the best, you fall to one Ice Beam.

Click to expand...

This is a check and not a counter. While Empoleon can live one Earthquake, it cannot survive two of them. Being slower than Flygon, it'll switch in, eat an Earthquake, then eat another one before it can act and die.

So for a real counter to Flygon:


Sylveon @ Leftovers
Ability: Pixilate
EVs: 252 HP / 252 Def / 4 SpA
Bold Nature
-Hyper Voice
-Wish
-Protect
-Heal Bell

252+ Atk Flygon Earthquake vs. 252 HP / 252+ Def Sylveon: 141-166 (35.7 - 42.1%) -- 90.4% chance to 3HKO after Leftovers recovery
4 SpA Pixilate Sylveon Hyper Voice vs. 0 HP / 4 SpD Flygon: 306-360 (101.6 - 119.6%) -- guaranteed OHKO

Doublade @ Steelium Z
Ability: No Guard
EVs: 252 Atk / 4 Def / 252 SpD
Careful Nature
- Iron Head
- Swords Dance
- Sacred Sword
- Shadow Sneak
Even with Doublade's Careful nature, it can switch in, tank two Hyper Voices from Sylveon, then one-shot with Corkscrew Crash off of Iron Head.

4 SpA Pixilate Sylveon Hyper Voice vs. 0 HP / 252+ SpD Doublade: 69-81 (26.6 - 31.2%) -- guaranteed 4HKO
252 Atk Doublade Corkscrew Crash (160 BP) vs. 252 HP / 252+ Def Sylveon: 438-516 (111.1 - 130.9%) -- guaranteed OHKO after Leftovers recovery