Possessed

The Possessed are a class of zombie-like monsters which appear in the Doom. They are similar to the zombies of Doom 3 in behavior and in their status as pure, unarmed cannon fodder. Possessed come in several varieties with wildly differing appearance, behavior, and difficulty- mainly four classes.

Possessed Scientists
Possessed scientists are the weakest class of Possessed. They are completely mindless and simply shuffle toward the player, aiming to batter them to death. Parts of their uniforms are melting into their flesh, and a large hole is situated where their nose and eyes once were. They are completely unchallenging and essentially only serve to be fodder for Glory Kills and the player's pistol.

Possessed Engineers
Possessed engineers are essentially Possessed Scientists with a unique character model- and an explosive tank fused through their chest. This means that they may explode if you are not careful fighting them.

Possessed Soldiers
Possessed soldiers, while still inhuman in behavior, are significantly more intelligent and challenging than possessed scientists. They still display a degree of tactical acumen, and battle the player with an automatic plasma gun in combat, fused into their right arm in the fashion of an arm-cannon. They wear flesh-melted UAC combat armor of sorts, giving them increased durability, but can still be killed with a couple shotgun blasts or other weapons. Their plasma guns can either fire in automatic mode, or charge a more powerful shot. They are the equivalent of the original Doom's zombiemen, or Doom 3's Z-SEC.

Possessed Security
Possessed security units are the most difficult possessed enemies. They are identical to Possessed Soldiers, but their plasmaguns behave like hitscan plasma-shotguns instead (uniquely making them the only hitscan enemies in the game), and they use a large, transparent energy shield in combat. They perform advanced tactics such as firing in defilade and dropping their shield to adopt a more accurate firing stance. This shield makes them frustratingly difficult to kill, especially since they can still fire their shotgun over the side of it. They are the equivalent of Shotgun Guys from previous games.

Codex data
"The Possessed are created in Lazarus Wave event, a phenomenon first discovered by Dr. Olivia Pierce during her Lazarus Project. While most of victims exposed to Argent biowaves will expire without further effect, some subjects will absorb traces of Argent Energy and enter state of posthumous vigor. Despite necrosis of the internal organs (with the exception of the brain), the victim continues to animate and exhibit a low order of sentience for weeks or even months after clinical death. Posthumous brain activity in the Possessed is limited to instinctive behavior. The Possessed are known to be territorial when confronted by the living. When isolated, they will often enter a dormant state of extended periods of time. They will stand, unmoving, for days or weeks at a time until presented with a live food source, or threatened by a predator."

- Codex entry