Sturdy

Summary

Sturdy is a Pokémon ability introduced in Generation III.

Effect:

Prevents the Pokémon from being knocked out in one hit, leaving it with 1 HP if its HP was full before the attack
Grants immunity to one-hit KO moves: Fissure, Guillotine, Horn Drill, and Sheer Cold
If the Pokémon is holding a Focus Sash, Sturdy takes precedence, and the item is not consumed

In Battle:

Acts as a built-in Focus Sash, ensuring that the Pokémon can survive at least one attack when at full HP
Allows a Pokémon to set up moves or retaliate after surviving a hit
Provides an opportunity to use status-inducing or strategic moves like Stealth Rock, Spikes, or Toxic
Particularly useful for setting up hazards or using moves like Endeavor
Can be nullified by multi-hit moves or indirect damage like Sandstorm, Hail, or entry hazards if the Pokémon isn't at full HP

Pokémon with this Ability:

Competitive Use:

Frequently employed on Pokémon that are meant to set up entry hazards or disrupt the opponent’s strategy
Provides security against unexpected powerful attacks, enabling strategic play
Often used in combination with moves that benefit from survival, like Explosion or Counter
Can be a surprise factor in battles, especially when opponents expect an easy knockout
Works effectively with Pokémon that have access to recovery moves or Leftovers to regain full HP

Interesting Facts:

Originally only provided immunity to one-hit KO moves until Generation V, when the effect was expanded to prevent being knocked out in one hit
Commonly found on Pokémon with high Defense stats, enhancing their role as defensive pivots
The ability's name reflects its function, providing resilience akin to being "sturdy"
Notably featured in the Pokémon anime, showcasing the dramatic survival against powerful attacks

When this Pokémon is at full HP, any hit that would knock it out will instead leave it with 1 HP. Regardless of its current HP, it is also immune to the one-hit KO moves: fissure, guillotine, horn drill, and sheer cold. If this Pokémon is holding a focus sash, this ability takes precedence and the item will not be consumed.

ruby-sapphire: Negates 1-hit KO attacks.
emerald: Negates 1-hit KO attacks.
firered-leafgreen: Negates 1-hit KO attacks.
diamond-pearl: The Pokémon is protected against 1-hit KO attacks.
platinum: The Pokémon is protected against 1-hit KO attacks.
heartgold-soulsilver: It is protected against 1-hit KO attacks.
black-white: It cannot be knocked out with one hit.
black-2-white-2: It cannot be knocked out with one hit.
x-y: It cannot be knocked out with one hit.
omega-ruby-alpha-sapphire: It cannot be knocked out with one hit.
sun-moon: It cannot be knocked out with one hit. One-hit KO moves cannot knock it out, either.
ultra-sun-ultra-moon: It cannot be knocked out with one hit. One-hit KO moves cannot knock it out, either.
lets-go-pikachu-lets-go-eevee: It cannot be knocked out with one hit. One-hit KO moves cannot knock it out, either.
sword-shield: It cannot be knocked out with one hit. One-hit KO moves cannot knock it out, either.
scarlet-violet: The Pokémon cannot be knocked out by a single hit as long as its HP is full. One-hit KO moves will also fail to knock it out.