Weapon (The Eyeless)

The Weapon was a device used in an intergalactic war.

Abilities
Not only could it destroy all traces of an enemy, it would destroy all traces that the enemy had existed as well as everyone who had ever even heard of them. When it was working as intended, it was capable of destroying all living things in the universe.

Inside the Fortress, the weapon resembled a humming cylinder of burnished metal, one metre long and ten centimetres wide, with no controls or inscriptions. However, more interesting things were going on in higher, lower, and sideways dimensions; when she held it in her bag, Alsa could feel something beneath, inside, and around the metal, as if it was eating away at her. In this form, the weapon was activated by touch. (PROSE: The Eyeless)

History
The Tenth Doctor said that its creators built it as a weapon of last resort, to be used "only when all was lost", since it would destroy not only its enemy but also its user. It ran on quantum physics, the observer effect, the superforce, vunktotechnology, and vundatechnology.

The Tenth Doctor believed that it needed to be destroyed to stop it from being used again, and he was only person left in the universe who could destroy the weapon, so he travelled to Arcopolis to deactivate it where it sat in the Fortress, where it had been left after it was used to destroy its creators and their enemy in the Last Battle of the Seventh Galaxy. As he endeavoured into the Fortress, he was attacked by ghosts, which could pull anything they touched out of reality, and the Eyeless, who had come to scavenge the weapon. The Eyeless activated the weapon, but it backfired, destroying them and leaving the Doctor alive. This led the Doctor to realise that the weapon had been malfunctioning: the ghosts were complex blast shadows left behind when the weapon annihilated them during the Last Battle; this also explained why the weapon hadn't destroyed the universe during the Last Battle, which the Doctor had previously speculated was due to a protective field around the weapon.

The Doctor and Alsa ultimately destroyed the weapon by dropping it into a plasma vent on an asteroid. There, it opened and something came out that the Doctor and Alsa couldn't look at; the thing couldn't survive in the universe, and with it, the weapon was destroyed. (PROSE: The Eyeless)