Cacodemon/Doom 3

The Cacodemon in Doom 3 has a very distinct appearance from it's classic iteration. It's overall body shape is a lot less spherical, instead taking the appearance of a floating taupe reptilian-like head, with multiple green eyes and long thin tentacles hanging from the bottom of its body and a brain clearly visible on the top of its forehead. They are characterized by a mysterious whirring sound they make when they are present.

The Cacodemon is usually found outside Martian surfaces, although they can be encountered in relatively close-quarter indoor areas, as long as the ceiling is sufficiently high. The Marine first encounters these floating demons in the Communication Transfer when a lone Cacodemon floating withing the Martian atmosphere, greets him after he opens the airlock.

Combat Characteristics
The Doom 3 version of the Cacodemon moves through the air faster than it's previous incarnations although it is still pretty slow relative to the player.

Like the original, it fires an energy ball in a straight line. This projectile is more missile based instead of being a simple purple/red plasma ball, 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 the lag for them to initiate such attack takes 2-3 seconds, which leaves them equally vulnerable in the process.

Cacodemons often appear in groups of 3 or more, although they can come in solo while being accompanied by lesser demons such as Imps and Z-Secs.

Tactical Analysis
The Cacodemon, despite its updates, is not a difficult foe to deal with. While it is harder to hit and closes in faster compared to the original version, the increased firepower in some of Doom 3's weapons allow them to be taken down much quicker than the classic Cacodemon. It can be killed rather quickly with sustained fire from the Chain Gun, 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 Shotgun also work well, as it takes two shots to take one down. The first shot will cause the Cacodemon to back away from the player, leaving it vulnerable as a result.

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.

The Cacodemon's energy ball can do heavy damage to the player, and they should be avoided or shot down at all costs. The Machine Gun and Plasma Gun are very effective for countering them.

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. Furthermore, their biting attacks can easily be avoided thanks to the large lag they have to go through to initiate the attack. 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.

Trivia

 * 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 from the classic games. It's also notable how many similarities the Doom 3 Cacodemon has to the Pain Elemental, so it is likely that the Cacodemon was originally supposed to have been a hybrid of two classic Doom monsters.