The Sentinel Hammer (also known as the Hellbreaker) is a weapon introduced in The Ancient Gods - Part Two DLC for Doom Eternal, and it also appears in Mighty Doom in a later update. It is a large, energy-based warhammer of Sentinel origin, which serves as a replacement for the Crucible from the base game.
The hammer originally belonged to Commander Valen and can be seen leaning against his chair when the Doom Slayer visits him during his exile in Hell. When the Slayer begins his pilgrimage to the World Spear, he comes across a projection of Valen who thanks him for putting his son to rest before giving him the Sentinel Hammer to use in the battles ahead. When Valen appears as part of the Night Sentinels army to support the Slayer's attack on Immora, he is wielding a weapon similar to the Sentinel Hammer, but with a blue energy head instead of red.
Uses
Doom Eternal
Using the Sentinel Hammer's "Sentinel Slam" momentarily launches the Doom Slayer up into the air before he comes crashing down, slamming the hammer into the ground and causing a shockwave around the point of impact. (The Hammer thereby allows the Slayer to emulate the ground-pound attacks of the Hell Knight, Dread Knight, and Baron of Hell.) Enemies caught in the shockwave are either temporarily stunned or killed outright, depending on their health level; either way, they will drop some ammo. Enemies frozen by Ice Bombs drop additional health during this time, while enemies set alight by either the Meat Hook or the Flame Belch drop additional armor.
The Sentinel Slam can also be used to slow already-staggered enemies, such as Marauders or Davoth. Doing so will turn their "Silver Stagger" state into a "Gold Stagger," greatly extending their vulnerability period. It can also be used on Armored Barons to delay the regeneration of their armor.
The Sentinel Hammer is recharged by destroying enemy weak points or by performing Glory Kills; each will restore half of a charge. Like the Crucible, each level in the DLC also has red-glowing tokens which can be picked up to instantly refill the Sentinel Hammer's charge.
Overall, the Sentinel Hammer is a versatile weapon that can be used much more liberally and stylishly than the Crucible. It can give the Slayer extra resources, leave powerful enemies vulnerable for retaliation, or just clear out a horde of demons when he needs some breathing room.
Mighty DOOM
In Mighty DOOM, the Sentinel Hammer is the fifth and ultimately final secondary weapon introduced into the game, and the only one that works as a melee weapon. The Sentinel Hammer is used manually with a 10-second cooldown, in which it is slammed onto the ground to generate area-of-effect shockwaves that natively inflict ice 
damage in a circle within the Slayer's vicinity, color-coded blue. With other upgrades, it can inflict other elemental effects that debuff enemy stats (green toxic 
damage that inflicts defense-reducing Corrosion and/or purple plasma 
damage that inflicts offense-reducing Malfunction), or gain higher reach and accuracy.
Upgrades
Doom Eternal
The Sentinel Hammer can be upgraded by completing the mandatory stage of each escalation encounter in the DLC. By the end of the DLC, the hammer should be fully upgraded.
- The first encounter on the World Spear unlocks the Ammo Boost upgrade, which causes enemies to drop more ammunition when damaged by the Sentinel Slam.
- The second encounter on Earth Reclaimed provides the Fire and Ice Boost, which causes flaming enemies to drop more armor and frozen enemies to drop more health when hit by a hammer slam.
- The third encounter on Immora provides the Extended Daze upgrade, which extends the duration of the hammer's stun effect.
Mighty DOOM
The possible 4 abilities the Slayer can obtain for the Sentinel Hammer temporarily for one run are as follows:
Hell Breaker: Jump to the nearest enemy before attacking with the Sentinel Hammer.
Lead Poisoning: Adds Toxic damage and applies Corrosion, weaking enemy defense.
Sentinel Slam: Sentinel Hammer creates an additional shockwave and attack radius is increased.
Static: Adds Plasma damage and applies Malfunction, weakening enemy attacks.
