Soul Cube

The Soul Cube is a fictional artifact and weapon from Doom 3. In the default keyboard settings, press the "Q" key to use the Soul Cube. Its name may be derived from the soul sphere item in classic Doom.

History
After the Martian race first encountered the forces of Hell at some point in their past, they ended up in a hopeless struggle against its demons. With whatever conventional weapons they had proving ineffective at stemming the horde, they eventually devised a plan using their greatest technology, which bordered on functional magic. Most of the survivors were sacrificed, and their souls were used to create the weapon that would turn the tide: the Soul Cube. With it, their single greatest champion, simply called "the Hero", (a take on the Doomguy's namelessness) took on the invading force singlehandedly and managed to seal the portal. Though "the Hero" didn't seem to survive since his burial chamber was found. He appears to be very tall, because his tomb is very long.

The Cube was then buried along with other artifacts near the Hero's burial chamber, in case anyone ever had to deal with the forces of Hell again.

During the game
Soon before the Mars invasion began, Dr. Betruger took the Soul Cube and went through the teleporter without authorization to have it contained in Hell. Thus, having the key to their defeat now in their hands, the demons invaded the UAC Mars Base.

The Marine receives the Soul Cube at the end of his trek in Hell, just after defeating the Guardian boss. After the Player obtains the Soul Cube, it gives a speech, with the most important words informing the user that they (the souls of the Cube) are "the Praeleanthor" and that they are the only way to defeat "Hell's mightiest warrior" (the Cyberdemon).

At the end of the campaign the fate of the Soul Cube is unknown. After defeating the Cyberdemon, it proceeds to travel into the dimensional portal and seal it off, causing lava to boil up to the top and solidify. The Cube was presumably destroyed (sacrificing itself) or trapped within the portal in order to destroy Hell's only link to our dimension.

Operation
The Soul Cube is powered with the life force liberated following any death, including humans and allies, at the hands of its current user. Five kills will leave the Cube ready and fully-charged, and it will then say, "Use us." An indication will be when the Cube is lit up at its five orbs (four on the side and one in the center). The Cube then displays a large intersecting collection of whirling circular blades, before zooming off to the target and damaging it with the said blade array. During its attack, the player's normal weapons replace its position at the helm. It also transfers the target's life force to the user, partially or completely healing any injuries the player may have, depending on the remaining hit points of the main target when the Cube strikes. The Soul Cube attacks intelligently; it always attacks the enemy with the largest amount of hit points within range, and homes in on the target. This targeting can be overridden by aiming the screen reticule at a particular target. The damage per Soul Cube attack is 1,000, and splash damage of 40 to adjacent enemies. The maximum health that the Cube can restore to the player is 99. The rate of restoration is 5 health points per interval, and two intervals per second. The Soul Cube will not restore damage taken after the attack begins, but before it is completed. Be aware that it is possible to launch the Soul Cube without a valid target, in which case the charge will be wasted at no effect.

Only the boss demons, like Sabaoth and Cyberdemon, can hope to survive even a single Soul Cube attack (4 attacks to be exact to kill the Cyberdemon), and even then, the Cube still performs a life force transfusion. The Cube then retracts the array and returns to the user's keeping, until its wielder inflicts enough deaths to re-energize it.

It should be noted that the life force absorption seems to be only needed to power the Soul Cube's movement and homing functions. When it is charged and idle, it occasionally displays its blades and spins for a brief period of time.

The Soul Cube does not attack monsters that are unaware of the user's presence, nor does it attack living humans, as seen in Nightmare mode where the player receives it at the beginning of the game.

Properties

 * It is immune to radiological scans of any nature, including X-rays and gamma rays.
 * Its atomic makeup cannot be analyzed for this reason.
 * It maintains a constant temperature of 98.8 degrees Fahrenheit (37.1 degrees Celsius), regardless of surroundings (which is, more or less, the natural, constant body temperature of a human being).
 * It levitates.
 * It is impossible to measure the weight or mass of Cube for this reason.
 * It is apparently completely immune to damage, at least from conventional sources.
 * Attempts to open the Cube have yielded no results.
 * It is not a perfect cube. Portions of it are ornamental-decorated, and one entire corner of the Cube has been cut into with ornamental sculpting that seems almost organic. A pair of triangular, flat surfaces extend from the bottom.
 * It is sentient with the souls used to create it.
 * It is apparently able to penetrate any type of armor, as the Cyberdemon at the end of the game cannot be harmed by any type of weapon except the Soul Cube (possibly meaning there is a magical shield surrounding the monster).

Strategy
The Soul Cube should be reserved for larger enemies, like the Hell Knight or Arch-Vile. Since the Soul Cube requires 5 souls, it is advisable to use it primarily on stronger enemies. This does not mean that the player should completely reserve using it when swarmed by small enemies like Trites or Cherubs. This is because the splash damage from the cube's attack is likely to dispatch several targets at once, and the availability of many tiny targets ensures that the soul battery is very easy to refill throughout the encounter.

As stated above, when charging the Soul Cube the best enemies to kill are ones with few Hit Points, such as the Trite, Tick, and Lost Souls. In nightmare mode, its is possible to kill living human to fuel up the Soul Cube, considered as merciless player.

Trivia
The concept of feeding a weapon with the "souls" of killed enemies might be inspired by the Doom Bible. At the ammo section, it was told that the demon-styled weapons (like the former Unmaker) used the "Killed humans" ammo.