Doom Eternal's Unmakyr can be a challenge to unlock, since you have to collect every Empyrean key from every optional Slayer Gate in the game. But once you do, you'll permanently have a super weapon that can stand beside the iconic BFG 9000.
The Unmakyr uses the same ammo as the BFG 9000, so use it sparingly. We used the Infinite Ammo cheat so we could rip and tear as much as possible to show off this powerhouse of a weapon.
The weapon originally appeared in Doom 64 as the Unmaker, which had its own set of secrets. You can see how that performed in this video right here, in a level which apparently ties Doom 64 to the story of Eternal.