The Nimons were large black-skinned humanoids resembling the mythical minotaurs. Their horns can shoot out blasts of energy. Nimons drained energy direct from their victims, leaving them as husks. The Nimons have mighty, rumbling echoing voices.
The Nimons could use an artificial black hole as a gateways from planet to planet. This technology was effective but not energy efficient. Due to their high energy needs, the Nimons undertook migrations they called the Great Journey of Life. Usually, one Nimon was sent to a planet, representing themselves as a god with advanced technology where it would construct a maze-like Power Complex, a building-sized labyrinth of circuitry designed to generate a new black hole which it then used to transport more Nimon to the planet, using capsules. The Nimons would then drain that world dry and move on.
Nimons were capable of using a psioninc mind beam to transfer their power and were able to use gravitic distortions, gravitational lensing and phasing energy through an event horizon. The effect was the gift of immortality onto another being.
The Nimons were one of many races that participated in the Millennial War against the Mad Mind of Bophemeral where they collaborated with the Osirians in dropping quantum collapsers on the insane computer intelligence.
When the Doctor and Romana stopped the Nimons they had used exhausted Crinoth and had moved on to Skonnos, home to the faded Skonnos Empire. The Nimons used the Skonnan Soldeed as their priest and demanded tribute of hymetusite crystals from the planet Aneth.
The Doctor later encountered the Nimons who were in contact with Sebastian Grayle influencing him to aid their invasion of Earth.