The Cacodemon in Doom 3, as compared to the original monster, is taupe in color, has a wider mouth, and has multiple green eyes, as well as some longer, thin tentacles hanging from the bottom of its body. Its brain is clearly visible on the top of its forehead. The Cacodemons are usually found in outdoor areas, although they can be encountered in relatively close-quarter indoor areas, as long as the ceiling is sufficiently high. They often appear in groups of 3 or more and are characterized by a mysterious whirring sound they make when they are present.
The Doom 3 version of the Cacodemon is no bloated ball of sloth as it flies rather speedily around this time and, as a consequence, is harder to hit and closes in faster.
Due to increased firepower in some of Doom 3's weapons, it can be considered "weaker" than the classic Cacodemon (it can be killed with merely two point-blank shotgun blasts or a second of sustained chaingun fire), however, it still takes two rockets, 1/3rd of a machine gun magazine, or more than a dozen plasma shots from the plasma gun to kill. Like the original, it fires an energy ball in a straight line at the player, although this projectile is yellow instead of purple and red, and sometimes it fires it in a somewhat wild direction, deliberately "missing" their target, which can confuse players.
Up close, the Cacodemon can bite the player, although this tends to leave it vulnerable to melee attacks as the delay between opening its mouth and biting is long enough to make it rather easy to dodge.
The Cacodemon, despite its updates, is not a difficult foe to deal with. It floats slowly enough and is large enough such that targeting it is fairly easy, and it can be killed rather quickly with either the Shotgun or the Chain Gun. The Chain Gun is often the most efficient, especially when there is a lot of open space that will allow for plenty of time to keep the aim focused on the advancing beast.
The Cacodemons are more dangerous in groups as they can surround the player and attack from occasionally unexpected angles (e.g. from above).
Its energy balls can also be destroyed in midair, like every other explosive projectile in Doom 3, and they are easy to hit because they travel in a straight line.
Its biting attack has some surprise value, but often it only leaves the Cacodemon particularly vulnerable to melee weapons, such as the fists, flashlight or the Chainsaw. The Cacodemon is one of the Doom 3 monsters that is actually fairly easy to defeat with either the fists or the flashlight.
Steady fire on the Cacodemon can destabilize the Cacodemon and stun it for a short time.
In Resurrection of Evil, the Super Shotgun is definitely a recommended weapon against them, as it can easily kill it with one blast.
- At some point in the development of Doom 3, the Cacodemon was supposedly able to spit Lost Souls at the player, like the Pain Elemental in Doom 2. It is also notable how many similarities the Doom 3 Cacodemon has to the Pain Elemental from Doom 2, so it is likely that the Cacodemon was originally supposed to have been a hybrid of two classic Doom monsters, like the Doom 3 Hell Knight is a hybrid of the classic Doom Baron of Hell and Hell Knight.