Just as the Netherworld and Horizon have their own supernatural creatures there are some that reside on Earth.
Witches are mortals with supernatural powers. Most mortals are stuck to the Earthly plane. However, Witches can draw power from the other planes. There are two types of witches. White Witches, Which are witches that use their powers for healing, potions, charms, spells, and Earth's natural energies. They draw their power from nature to keep balance between light and dark. Meanwhile, Dark Watches study necromancy, demonology, dark incantations, and invocation of spirits. Their powers come from beyond the grave. However, just because they are a dark witch doesn't not make them evil. Most dark witches live in isolation away from anyone.
Warlocks are mortal men who practice dark magic. They use dark curses and spells and have mastered the dark arts. Unlike witches, warlocks are completely evil. They aim to control everything and have complete dominance over whatever they please. They are very dangerous and often help the demons with fighting the angels.
A true elemental is someone born of Angel and mortal parents. They are very powerful and have not only the supernatural energy from Horizon, but they also have the natural energy from the Earth. They can manipulate the water, earth, fire, and air that gives them their power. The elemental's human emotions are what generates their powers and causes them to be able to use them. Though the elemental power tends to turn toward the darkness, the elementals are not born evil. Since the elementals are so powerful if a demon eats their soul and gets some of their power the demon and can cause huge problems for the legion. For most elementals , only a mortal can touch them without harm. If a Demon or an angel were to touch them they would die. they need special gloves called Sparks to be able to touch the child without harm. This does not affect Kara since she and elemental, other angels and demons can touch her because she is born of fallen angel and guardian parents.
Some elementals are born of Demon and mortal parents, or at least from a fallen Angel who became a demon. In this case the elemental essence is no dominant and very hard to detect. This can cause the elemental child to never find out what they are and lead a normal life. However, the demon can still tell if they are elemental and makes the child a target.
Another type of elemental is where the child was born from Sanskrit and fallen angel parents. This is not as powerful as a full elemental but the child is still dangerous.