Counter

Samurott-Hisui @ Mystic Water
Ability: Sharpness
EVs: 252 Atk / 4 Def / 252 Spe
Tera Type: Water
Jolly Nature
- Swords Dance
- Razor Shell / Aqua Cutter
- Ceaseless Edge
- Aqua Jet / Sucker Punch

Wo-Chien @ Leftovers
Ability: Tablets of Ruin
Tera Type: Ghost
EVs: 252 HP / 252 Def / 4 SpD
Relaxed Nature
- Giga Drain
- Knock Off
- Leech Seed
- Protect

resists all attacks so it can freely switch in and not be pressured at all by

even after it swords dance on the switch. Giga drain here is able to heal back almost all of the health lost from an attack. The important parts of the set for wo chien are max defense and health and having giga drain. The other moves and the tera are not important here.
After 1 SDs here are some calcs
+2 252 Atk Mystic Water Sharpness Tera Water Samurott-Hisui Razor Shell vs. 252 HP / 252+ Def Tablets of Ruin Wo-Chien: 140-165 (37.4 - 44.1%) -- guaranteed 3HKO after Leftovers recovery
+2 252 Atk Mystic Water Sharpness Tera Water Samurott-Hisui Razor Shell vs. -1 252 HP / 252+ Def Tablets of Ruin Wo-Chien: 209-247 (55.8 - 66%) -- guaranteed 2HKO after Leftovers recovery
+2 252 Atk Sharpness Tera Water Samurott-Hisui Ceaseless Edge vs. 252 HP / 252+ Def Tablets of Ruin Wo-Chien: 75-89 (20 - 23.7%) -- possible 6HKO after Leftovers recovery
After 1 SD and Defense Drop or Crit
+2 252 Atk Mystic Water Sharpness Tera Water Samurott-Hisui Razor Shell vs. 252 HP / 252+ Def Tablets of Ruin Wo-Chien on a critical hit: 209-247 (55.8 - 66%) -- guaranteed 2HKO after Leftovers recovery
After 1 SD and Defense Drop Crit
+2 252 Atk Mystic Water Sharpness Tera Water Samurott-Hisui Razor Shell vs. -1 252 HP / 252+ Def Tablets of Ruin Wo-Chien on a critical hit: 314-370 (83.9 - 98.9%) -- guaranteed 2HKO after Leftovers recovery
And meanwhile
0 SpA Wo-Chien Giga Drain vs. 0 HP / 0 SpD Tera Water Samurott-Hisui: 218-260 (67.9 - 80.9%) -- guaranteed 2HKO (29.1 - 34.7% recovered)
After giga drain and leftover recovery Wo Chien heals almost all of the damage taken from non crits after a SD. Even after a crit it only takes about a net total of about 25% health lost. One crit is fine since you still win since the next attack will only deal at most 66% (assuming they got a defense drop on Wo Chien the last hit). The only sequence that actually kills is a tera water crit + defense drop razor shell into a crit razor shell. And if there are max spikes and rocks up then you still win since you start at 68.5% (37.5% lost from hazards, 6% healed from leftovers) and without a crit the max damage tera water Razor shell after a SD is 44.1% and you heal at least 35.1% from giga drain and leftovers. This means after the first giga drain you have at minimum 59.5% health which is more than enough (not accounting for a crit).
All of these calcs are including tera water since without tera water giga drain heals more than razor shell would deal after a SD (see below) and all are accounting for a SD on the switch since any non SD move on the switch just means it cannot deal that much damage in the long run to wo chien after it is in. SD + Razor Shell + Razor Shell is more damage then Razor Shell + Razor Shell + Razor Shell.
Non Tera Water after a SD
+2 252 Atk Mystic Water Sharpness Samurott-Hisui Razor Shell vs. 252 HP / 252+ Def Tablets of Ruin Wo-Chien: 105-123 (28 - 32.8%) -- 85.5% chance to 4HKO after Leftovers recovery
Non SD Razor Shell
252 Atk Mystic Water Sharpness Samurott-Hisui Razor Shell vs. 252 HP / 252+ Def Tablets of Ruin Wo-Chien: 52-62 (13.9 - 16.5%) -- possible 9HKO after Leftovers recovery
Non SD Razor Shell Tera Water
252 Atk Mystic Water Sharpness Tera Water Samurott-Hisui Razor Shell vs. 252 HP / 252+ Def Tablets of Ruin Wo-Chien: 70-83 (18.7 - 22.1%) -- possible 6HKO after Leftovers recovery
(This is the first one of these I have posted so if I did something wrong or made a mistake anywhere please let me know so I can fix it :) thanks!)