Mortal blow

Instant death attacks are a class of special attacks from Super Mario RPG: Legend of the Seven Stars. The term refers to any special attack that can instantly down a party member, regardless of either the party member's or the enemy's stats (such as Hit Points, attack, defense, etc.). Attacks of this variety include Magnum and Shaker. Instant death attacks can be blunted by pressing "A" at the right time during attack, allowing the party member to keep either one HP or all of their Hit Points. Certain accessories, such as the Jinx Belt, Safety Ring and the Quartz Charm, can prevent instant death attacks from having any effect.

Instant Death Attacks

 * Blazer - Blaster, Big Bertha
 * Fear Roulette - Ding-a-Ling
 * Magnum - Smithy (Tank Head)
 * Migraine - Pulsar, Body
 * Psyche! - Cluster
 * Scythe - Glum Reaper
 * Shaker - Boomer
 * Silver Bullet - Jinx

Other Kinds of Instant Death
The term 'Instant death' can also refer to anything in a video game that causes a character to be defeated instantly, no matter what conditions the given character is in. Some examples are getting crushed in Super Mario Galaxy, touching lava in the Mario 2D platformers, getting eaten by a Bubba or Big Bertha in Super Mario 64 and its remake, or falling into an Abyss. Also, any move in an RPG game (such as the Paper Mario games) that causes the attacked character to lose all of its HP in one hit can also be considered an 'instant death' attack.