Cyberdemon/Doom 3

"Witness what will be unleashed on Earth!"

- Betruger

The Cyberdemon is the final boss and most powerful monster of Doom 3. It is found at the Primary Excavation Site, where it stands guard over the massive Hell Hole. It stands roughly 20 feet tall, more than 3 times as tall as a human soldier. Like its original counterpart, the Cyberdemon attacks by firing a salvo of 3 consecutive rockets from its arm-mounted rocket launcher. Unlike the original version, it now has a melee attack as well: the monster can stomp on the player, killing them instantly.

Unlike its original counterpart, it cannot be hurt with conventional firepower; instead, the player has to utilize the most powerful weapon in Doom 3, the Soul Cube, to kill it. The Soul Cube states that only it can kill "Hell's mightiest warrior" presumably referring to the Cyberdemon. It takes 4 shots from the Soul Cube to kill the Cyberdemon. Fortunately, there are plenty of lesser demons on the level that can be killed to charge the Soul Cube.

While the Cyberdemon overall retains it's appearance as a minotaur-like giant, there are some differences of this new incarnation of the monster compared to its classic counterpart. This incarnation has a long tail, extending from the machinery on its back, and both legs are mechanical - as opposed to its original version, whose only mechanical leg was the right one. Another noticeable difference is that its rocket launcher is now located on the right arm instead of the left one.

The Cyberdemon did not make an appearance in the expansion pack Resurrection of Evil, so the one that was killed at the end of Doom 3 was presumably the only one.

The Cyberdemon is also the only monster from the original games to be a boss.

Strategy
The basic strategy for taking down the Cyberdemon is to always be on the move. Do not stay for too long in one place for any reason or the Cyberdemon will nail you with its rockets. Your stamina does not decrease near the Hell Hole, so take advantage of this and use sprint constantly. The Cyberdemon's rockets are fast, powerful, and long ranged, but fortunately the rocky spires around the Hell Hole prevent the Cyberdemon from getting a clear shot at you. However, do not get too close to the ledges as the blasts from the rockets can knock you into the Hell Hole to your death. Also, do not even think about going near the Cyberdemon: its melee stomp will crush you instantly.

Throughout the battle, you will be constantly attacked by Imps and Maggots, which will either teleport in or come crawling out of the Hell Hole. You want to kill these guys as fast as possible to get your Soul Cube operational. Use your Rocket Launcher or the BFG to one-shot these demonic lackeys. Don't worry too much about picking up any health units on the ground, since the Soul Cube will heal you. And, remember, always stay on your feet and keep out of the Cyberdemon's line of sight until the Cube is ready.

Once your Cube is powered up, turn around and face the Cyberdemon itself. As soon as the Cube has been launched, get out of the Cyberdemon's line of sight and start running again. Be sure your targeting reticle is focused on the Cyberdemon before launching the Cube. If there's an Imp or a Maggot nearby, the Cube may end up going for it instead of the Cyberdemon, thus wasting your shot.

After four hits with the Soul Cube, depending on the difficulty, the Cyberdemon will go down and you win the game.

Trivia

 * The Cyberdemon can be found in the game files of the Doom 3 expansion, Resurrection of Evil, but when it is spawned (for example by using a cheat code), the Cyberdemon appears to be vulnerable to regular weapon fire.
 * The Cyberdemon is referred to as "Hell's Mightiest Warrior" by the Soul Cube, although the Maledict has more hit points. This is likely because, unlike the Cyberdemon, the Maledict is vulnerable to conventional weapons.
 * In the final cutscene of Doom 3, the Soul Cube cuts off one of the Cyberdemon's legs, the one opposite the rocket launcher. This may be a callback to Classic Doom games, where the Cyberdemon had one robotic arm and one robotic leg. However, the arm and the leg are switched from the original version (the cut-off leg is on the left instead of the right). Since the Soul Cube killed the Cyberdemon immediately after its leg becomes amputated, there was never a chance for its leg to be replaced by machinery. Both of the Cyberdemon's legs are robotic this time, instead of just one.
 * If spawned in some places, the Cyberdemon will become stuck because it will have its body trapped in the ceiling. This is rather annoying, as it is very difficult to walk past the Cyberdemon without noclipping through it.
 * If noclip is used to get close and you punch the Cyberdemon, blood will come out of the robotic parts.