Home Planet: Earth
Life Form: Humanoid pig
Info: When the Daleks wished to cultivate humans into a new Dalek/human army, they would only chose those with high intelligence. Anyone who did not meet their standards would be changed into Pig Slaves instead.
When changed, the pigs have no memory of their past lives, and are less intelligent, simply following orders. They are extremely aggressive and savage creatures. However, they are also vulnerable and have very short lifespans, only lasting up to a few weeks. Post-mutation, Laszlo still retained most of his memory and personality since he managed to escape before the process could be completed.
Episodes appeared: Daleks in Manhattan, Evolution of the Daleks
Home Planet: Unknown (possibly Mutter's Spiral)
Life Form: Near humanoid
Info: The Plasmavores were a race of blood-sucking near-humans. They were commonly criminals, murdering people across the galaxy. They needed blood to survive as their bodies absorbed a lot of salt. Some Plasmavores made use of Slabs to restrain their victims before killing them.
The fact that they were near-human helped them to hide, as they could blend in with humans on Earth. When they drank Human blood, they could assimilate its properties into their own systems and fool alien scanners (such as the Judoon's) into seeming Human.
Episode appeared: Smith and Jones
Home Planet: Pyrovilla
Life Form: Molten Golems
Info: Their ship fell to Earth thousands of years ago, shattering them into dust. The 62 AD earthquake caused by Vesuvius re-awakened them, and they began possessed humans.
Although their home planet (stolen temporarily by the Daleks) was resored, the Pyroviles were supposedly destroyed in the AD 79 eruption of Mount Vesuvius.
Episode appeared: Fires of Pompeii
Home Planet: Around Mutter's Spiral
Life Form: Humanoid aracnid
Info: The Racnoss were an ancient race from the Dark Times and were wiped out by the Fledgling Empires over 4.6 billion years ago. However, one spaceship survived, creating the Earth around its self and going into hibernation.
Due to Torchwood attempting to drill to the centre of the Earth. This Empress of the Racnoss in her webstar was reawakened. She used the River Thames as a method of manufacturing Huon Particles to awaken the baby Racnoss at the Earth's core. She is now believed to be dead, as her webstar was shot down.
Episode appeared: The Runaway Bride
Home Planet: Outside of time (the vortex)
Life Form: Temporal predators
Info: Reapers are linked to Time itself. They would search out disturbances in time, such as paradoxes, leave the time vortex and "sterilize" the area by devouring everything, with older objects and sentient beings being the tastiest and more interesting.
They engulf their "food" in a flash of light, leaving no traces. Despite these powers, one in the real world, they become material creatures, and can be blocked. They cannot pass through solid objects, but as damage to Time accumulates, it allows them easier entry. The presence of Reapers would seem more common as, since there are no other Time Lords to prevent temporal paradoxes, they happened with more frequency.
Episode appeared: Fathers Day
Home Planet: Unknown
Life Form: Robotic
Info: The Spider Robots were used by Lady Cassandra for sabotage and later on for spying. They were transported on board Platform One within small metallic orbs, only emerging when the coast was clear.
On their own they don't seem to be very strong or dangerous, more like simple scouting droids, for small repair work and maintenance. However, they can be formidable in large groups, using their superior numbers to take out unsuspecting life forms. Usually though, they seem to work on their own, using their intelligence rather than strength to murder.
Episodes appeared: End of the World, New Earth
(Continued here: S-U)