Deathblows in Sekiro: Shadows Die Twice allow the player to fatally wound an enemy, making them die instantly. This usually occurs when an Enemy's Posture has been depleted, or when you take them by surprise under the right conditions. Certain types of enemies (Bosses and Mini-bosses) must be subjected to multiple Deathblows over the course of a fight.
Deathblows are executed by pressing the regular sword attack button; a large red circular icon appears over the center of an enemy when Sekiro can Deathblow them. Deathblows come in two main types: Deathblows performed in combat by depleting an opponents Posture and Deathblows performed in stealth by sneaking up on an unaware enemy and striking them from an unexpected direction.
When an enemy's Posture gauge is filled up completely or their Vitality bar depleted, he is vulnerable to a Shinobi Deathblow. At least one of this type of Deathblow is required to defeat Bosses and Mini-Bosses, though the player may perform them against any enemy.
Certain rare enemies classed by the game as Bosses enemies require an additional "Finisher Deathblow" in order to be defeated, which is executed in the same manner that a regular Deathblow is but which plays a special animation unique to the specific Boss in question. This Finisher Deathblow can only be performed once all of the enemy's Deathblow markers are gone; the window to execute it becomes available immediately following the prior Deathblow. Failing to execute the Deathblow awards the enemy a single Deathblow marker back and the player must once again bring the boss down in order to try again. The window is significant enough that even if you forget about it you have more than enough time to react to it; its only real purpose is to play a cinematic finisher animation.
This Deathblow can be performed by sneaking up to an unaware enemy and attacking them from behind. Enemies will generally hear Sekiro once he gets close enough to perform this Deathblow, so the player only has about a second or two to press the attack button before the enemy turns; fortunately, even enemies in yellow alert can be backstabbed in this manner so as long as the player attacks them quick enough he will succeed.
Ledge Hang Deathblow
A Ledge Hang Deathblow is a type of Stealth Deathblow that can be performed on unaware enemies from below them. While hanging from a cliff or ledge below where an enemy is standing, shimmying over so that you are just below them will make them vulnerable to this Deathblow.
This Deathblow may be performed mid-air while leaping at an unaware enemy from high in the air. It can also be performed even in combat against certain enemies which crawl flat along the ground, like lizards.
Wall Hug Deathblow
A Wall Hug Deathblow is a type of Deathblow that can be performed on unaware enemies. While undetected and hugging a wall, lie in wait for a passing enemy. When the enemy has nearly passed by, he will be vulnerable to this Deathblow.
An Anti-air Deathblow is performed on enemies which leap high up in the air. This technique is not available to Sekiro from the start, nor can it be unlocked via Skillpoints; instead, a scroll to teach it can be purchased from Blackhat Badger for 1200 Sen. This does not work on main bosses, but does on some mini-bosses that leap around such as the Shichimen Warrior.