Soul Cube/Doom II RPG

The Soul Cube is a weapon in Doom II RPG that instantly kills any enemy, after having killed five enemies. Once used, the gauge goes back down to zero, and needs five more kills in order to recharge.

Background
"We are many, we are one; we are the Praeleanthor, you know us as the Soul Cube."

The Soul Cube is powered with the life force liberated following the death of any enemy, 5 kills will leave the Cube fully--charged and ready to kill any target in 1 shot.

Souls are collected for the spiritual potentiality matrix of the Soul Cube.

Behind the scenes
Interestingly, the Soul Cube seems to know of the Heroes of Doom RPG, and the heroes of Doom RPG know of the Soul Cube. This may be a reference to UAC's previous research on the Soul Cube in Doom 3.