The Blood Punch is a new type of melee attack introduced in Doom Eternal. Unlike the standard melee attack, the Blood Punch must be charged by performing Glory Kills on enemies. It acts as a highly powered-up melee punch performed using the left fist of the Slayer.
The basic melee attack in Doom Eternal is practically useless, taking 90-100 strikes to cause a basic Zombie to enter its Glory Kill state. Blood Punch powers this up to an attack that can kill lesser enemies instantly within a significant radius and deals serious damage to larger ones.
The effect of a Blood Punch is a pair of circular AoEs centred on the Slayer: within the inner high-damage circle, all enemies killed will drop health. The outer circle is a "shockwave" which deals inferior damage but can still kill most Fodder enemies instantly, has a falter effect on larger enemies, and does not cause enemies to drop health by default.
Blood Punch is first unlocked in the second level, Exultia, after the first major enemy encounter. The pickup is represented as a large golden gauntlet, and cannot be missed. It is provided with a full charge when acquired. It will be upgraded over the course of the game as the player defeats bosses and kills Hell Priests.
By default, a Blood Punch requires two Glory Kills on any enemy type to charge: an indicator is provided above the health and armor bars in the HUD to show the current charge level. The charge will only be expended if the Slayer's fist strikes something that can actually receive damage: simply swinging at empty air will trigger a standard melee attack, and Blood Punch is also not triggered by hitting a breakable wall.
Blood Punch pickups are sometimes found later in the standard campaign and much more commonly in The Ancient Gods - Part 1. These are similar in appearance to the initial Blood Punch upgrade found in Exultia but much smaller. Picking one up instantly charges a Blood Punch. Killing a Spirit will drop a Blood Punch pickup.
A Blood Punch will deal additional damage to enemy weak points in a similar manner to the Heavy Cannon's Precision Bolt, the Combat Shotgun's grenade launcher and the Ballista's Arbalest mode. In general a single Blood Punch will destroy all of the weak points of an Arachnotron, Revenant or Mancubus, and instantly removes all of the armor of a Cyber-Mancubus.
Blood Punch also has significant effects on shields: unlike the Plasma Gun it does not cause them to explode and deal AoE damage, but it will bring down the shield of a Carcass in one hit. It has the same effect on the shield of an Archvile, though it still cannot break the shield of a Marauder.
Finally, Blood Punch deals additional damage to certain enemies: Pinkies and Spectres will typically die in a single hit even if struck from the front (though a Pinky boosted by an Archvile, Buff Totem or one that spawns Empowered may survive such a hit) and the "sled" of a Doom Hunter similarly takes more damage from Blood Punch than other sources. The Khan Maykr boss requires Blood Punches to "finish" each of her health bars and prevent her from regenerating.
As well as these storyline upgrades, there are two Sentinel Crystal upgrades that affect the behavior of the Blood Punch, and one Rune. The Sentinel Crystal upgrades "Health for Blood" and "Armor for Blood" respectively mean that once at 100% health or armor, additional pickups will charge Blood Punch if it is not filled. The Rune "Punch and Reave" upgrades Blood Punch so that enemies killed by the shockwave of a Blood Punch will drop health, as opposed to only enemies within the primary damage area.
The Ancient Gods - Part 1 adds a new Support Rune that affects Blood Punch, called "Desperate Punch." This will double the damage of a Blood Punch if it is triggered when the Slayer's health is 75 or less. Armor does not affect its ability to trigger, only health.