Hell guard

The Hell guard is a golem-like monster in the Doom inhabited by a small, worm-like demon which controls the larger body. Three of these entities serve as the guardians of the crucible at its resting place deep inside the Titan's Realm, and act as the boss of that level.

Tactical analysis
Hell guards are permanently protected by shields that only dissipate when they attempt to attack.

They can be staggered by detonating the charging yellow orb right before multiple orbs are fired toward the player in a cone.

They are weak versus explosive ammunition.