Crucible

The Crucible, a central plot item in Doom (2016), is an artifact from Argent D'Nur which wields mysterious control over the Argent energy reserves of Hell, capable of shutting down&mdash;and apparently reactivating&mdash;the source of that energy known as the Well. Samuel Hayden sends the Doom marine back into Hell with the purpose of reclaiming the Crucible, stating that its recovery is the only means to seal the Hell portal which was opened at the Argent Energy Tower by Olivia Pierce. The Doom marine actually sees the Crucible several times before finding it, in bizarre psychic visions which plague him during his journies between different areas.

True form and origin
The Crucible is found at the end of the Necropolis within the Hell guards' arena, where it is stored inside a retractable pillar. Defeating all three of the Hell guards allows the Doom marine to at last reclaim it, after which he experiences a vision of the Night Sentinels in a green, ghostly form. It appears as a compact skull-like ornament connected to a base by a central handle. The true form of the Crucible however is not directly revealed until the end of the game, when it is taken from the marine by Dr. Hayden forcefully while he is being held captive by the tethering device. Stating that he is unable to kill the marine, Hayden still manages to activate the Crucible in a threatening display, revealing it to be a weapon in the form of a sword with an Argent energy blade, inscribed with blazing red runes. This sword evidently once belonged to the Doom Slayer, and was probably either given to him by the "wretch" whom was also said to have forged or upgraded his Praetor suit, or was created by the Seraphim, who were said to have armed him with "sword and shield of adamantine strength."

While an important item in the story, the Doom marine never gets to wield the Crucible as a weapon. It is currently presumed that a sequel or update to the game may involve the marine attempting to reclaim it from Hayden, who intends to use it to further his Argent energy research and further endanger mankind in the process.

If a stone tablet in Samuel Hayden's office is carefully examined, it can be found to display an etched picture of the Crucible in its true form. This is the only hint that is given of it before its appearance in the game's ending.