The user is able to deal extremely damaging attacks to the enemy dealing double the damage or causing very lethal pain or fatal wounds. This can be done with an effective or a precise strike to an opponent's body, or with a special ability that happens to be the enemy's weakness. Highly advanced users can take down their opponent in one attack.
Pokémon with the Merciless ability (Pokémon); only against poisoned opponents
Sonic the Hedgehog (Sonic the Hedgehog series)
Various Characters (Soul series)
Mario (Super Mario)
Younger Toguro (Yu Yu Hakusho)
Tien Shinhan (Dragon Ball series) deals a critical blow to Yamcha's leg using the Super Knee Uppercut, thus breaking it.
Son Goku (Dragon Ball series) uses the Kaio-ken Finish...
...to deliver a critical blow to Nappa, breaking his back and permanently crippling him...
...and used Miracle Blow to punch through Broly's stomach, reopening his childhood wound and dealing a critical blow onto him, physically and mentally.
After tiring out Vegeta during their fight, Android 18 (Dragon Ball series) was able to break his arm, greatly impeding his fighting abilities.
Android 17 (Dragon Ball series) deals a critical blow to Piccolo's chest and spine.
Son Gohan (Dragon Ball series) uses the Soaring Dragon Strike to deliver a sharp hook punch to the Cell's stomach before follows up with a swift uppercut to his chin, sending Cell reeling back and severely injuring him...
...and was also able to deliver a powerful kick to his body, not only greatly injuring Cell, but also have him eventually regurgitate Android 18 and revert back to his Semi-Perfect form.
Son Gohan (Dragon Ball Z: Bojack Unbound) using his Quiet Rage to punch right through Bojack's stomach, dealing a critical blow.
Oboro (Gintama) infusing his ki into his Hakkei strike to deal a critical blow to Gintoki's meridian.
Terra's (Kingdom Hearts series ) entire fighting style is centered around this ability.
With his Critical Impact fighting style, Terra (Kingdom Hearts series) can utilize the Zantetsuken technique to perform an impossibly fast strike that deals a devastating amount of damage.
Kain (Legacy of Kain) deals a single critical strike to an opponent by using the Fury Dark Gift.
X and Zero (Mega Man X series) can use their Special Weapons to expose their opponent's weakness and deal with great damage to them.
Channeling his chi into his hands, Danny Rand/Iron Fist (Marvel Comics) can deal crippling blows to his opponents and structures...
...such as the H.A.M.M.E.R. helicarrier, for example...
Jotaro Kujo's Stand, Star Platinum (JoJo's Bizarre Adventure Part III: Stardust Crusaders) dealing a powerful and crippling punch to DIO's vampiric head!!...
...and later finishes off The World.
Like many characters, Yoshimitsu (Soul series) can deliver attacks that critically damage his opponents.
During his first fight with Yusuke and Kuwabara, Younger Toguro (Yu Yu Hakusho) was able to land a critical blow to Kuwabara, causing him to cough blood and slamming him into a wall...
...and with his 100% power, he dealt a critical blow to Yusuke's arm and leaving him writhing in pain.