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 one-hit down a party member, regardless of either the party member's or the enemy's stats (such as Hit Points, attack, and defense). 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 HP. If the timing was perfect, the party member will keep all HP as though nothing happened, but if it is slightly off, the party member will still survive with a single Hit Point. 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 references of instance 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 touching lava in the Mario 2D platformers, getting crushed, 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 HP in one hit can also be considered an 'instant death' attack.