Crucible

The Crucibles are powerful demonic artifact featured in Doom (2016), discovered via hallucination in the Lazarus Labs. In Doom Eternal one of the Crucibles is the Doom Slayer's sword.

The Crucible of the Doom Slayer is partly destroyed when the Doom Slayer breaks the blade to finish off the Icon of Sin, leaving only the handle intact.

The crucible blades are the only thing that can vanquish the Titans.

Description
The Crucible is a large dagger-like sword with a handle that looks like a skull and lower part modeled after Mancubus eye. It has an ability to absorb huge amounts of demonic energy.

The Crucible first appears via hallucination in the beginning of the game when the Doom Slayer touches the Praetor Suit, and again after the player touches the Helix Stone where an altar with a strange artifact and a source of demonic energy can be seen. Physically it appears at the end of level The Necropolis guarded by the Hell Guards, which must be defeated in order to reach the artifact. After this moment The Crucible appears at the end of Argent D'Nur, where player uses it to close 3 sources of energy powering the portal between Hell and UAC Base on Mars.

Samuel Hayden appears to know far more about The Crucible than he lets on; when he confiscate it from the Doom Slayer at the end of the game he knows how to 'activate' it, causing a large plasma-red and sword-like blade bearing demonic runes to manifest from within the artifact.

Doom Eternal
There are two Crucibles in Doom Eternal. The one from 2016 powers the Fortress after Khan Maykr cuts the power source and unleash demons upon the Slayer, the other which originally belongs to Doom Slayer can be used as a weapon in Doom Eternal. The YouTuber Gmanlives also explained how The Crucible would work in combat. The Crucible contains three "charges" located just below the crosshair, The Crucible acts much like the chainsaw in its ability to instantly kill any Demon for the cost of one of the charges, and a red sword pick-up is used to refill a single charge.