Nimons are tall, lanky black creatures; on their oversized bull-like heads are two red eyes and a pair of tall yellow horns. They have three wide fingers and wear gold loincloths. Nimons are also surprisingly graceful. Their voices are like an electronic growl, and they roar loudly when angry. The horns double as a weapon, and with its head lowered, a Nimon can fire a spiralling beam of energy from them. A yellow beam stuns, and a red beam kills. The Nimons feed by ingesting the binding energy of organic compounds like flesh, and they keep people in suspended animation for this purpose, like a sort of larder. When this life force is drained from their victims' bodies, only a husk is left behind.
Nimons are like a plague of locusts, swarming from planet to planet, sucking each one dry before moving on to the next. This cycle is known as the Great Journey of Life and is of paramount importance. Nimons multiply during the Great Journey of Life, increasing their destructive force and turning them into an even more widespread threat.
The Great Journey of Life follows a basically set pattern. One Nimon arrives on the target planet in an egg-shaped space capsule and promises technology, peace and prosperity to the inhabitants. It claims to be the last survivor of its race, making the inhabitants think that there is only one Nimon. In return for its help and guidance, it asks only that it be given a tribute - regular gifts of seven human sacrifices and seven hymetusite crystals. These blue crystals are highly radioactive, emitting ultra radiation level Q 7.325. The Nimon gives its servant an energy staff which can be used as a weapon. It constructs a power complex that resembles a positronic circuit, protected by a hemispherical defense shield, which functions as a giant transmitter. A fixed gravity beam, transmitted through the horn-like antennae, tracks matter to one point in space - creating a gravity whirlpool - and collapses it to a singularity. This creates a gateway to hyperspace through which the space capsules can travel. A hyperspatial tunnel is established between the new black hole and the one created from the previous victim planet, with the energy beam providing motive power. On the inside of the power complex is a maze with a warbling sound in the background. The walls move when the circuit-like power complex is in operation, causing the paths to constantly change, and these alterations are heralded by a louder warbling noise. The exit is disguised as just another wall, and the maze can only be entered by the Nimon's servant, possibly because of the energy staff. The Nimon purifies its hymetusite crystals in a nuclear furnace - its controls, amusingly, seem to be labelled in English. When all of the crystals have been processed, the Nimon begins bringing the others through the hyperspatial tunnel so that they can begin draining the planet. The other Nimons rely on the power plant on the next planet to pull them through, although as a final contingency plan, they can convert the planet's matter into energy. Once this process has begun, it cannot be stopped, and will cause the entire planet to explode - although by this point, it has been drained of all its energy anyway, and nobody is left behind to care.
On Skonnos, the Nimon worked with Soldeed, a great scientist and enginner and leader of the planet. Skonnos had just emerged from a civil war that wiped out all but the army, and the Nimon promised that it would enable Soldeed to conquer a galaxy by bringing power from the stars to power a new fleet of Skonnon warships. Enraptured with the idea that "Skonnos shall rise and conquer", Soldeed eagerly did whatever the Nimon asked. This involved bringing sacrifices from the planet Aneth, more popularly known as the bearers of Aneth's tribute to the Nimon. Soldeed thought he was using the Nimon, and was therefore quite surprised when two more Nimons appeared in the power complex. Skonnos was to be their new home, the next step in the Great Journey of Life, and the Nimons were eager to begin their migration. As Romana told Soldeed: "They're parasitic nomads who have been feeding off your selfishness and gullibility!" The Nimons had just come from the planet Crinoth, and during the Doctor's investigation of the complex, he accidentally sent Romana there in one of the capsules. On Crinoth, Romana learned that a dark blue stone called jasonite, which carried a powerful electromagnetic charge, could modify the beam in an energy staff to stun the Nimons when it was wedged between the staff's four prongs. With the help of Romana, the modified staff and some of the would-be sacrifices, the Doctor disabled the Nimons' system. Soldeed, in retaliation against the Nimons, set their reactor to critical. With most of the Nimons stranded on Crinoth, the complex exploded, and soon Crinoth exploded as well...ending their Great Journey of Life.
