Phoenixes are powerful beings who appear human. They possess the ability to incinerate things through touch and are immune to conventional methods of killing humans. They combust upon death and form a pile of ashes. Their ashes can be used to kill, Eve, the Mother of All. Iron is one weakness and they can be killed by the colt.
Rakshasa: A demon or unrighteous spirit in Hinduism that feeds on human flesh. They are shapechangers and magicians, and often appear in the forms of humans, dogs, and large birds. They can make themselves invisible and can not enter a home without being invited. According to the Ramayana, an ancient Sanskrit epic, they were created from the Foot of Brahma, the Hindu God of Creation. Many Rakshasa were particularly wicked humans in previous incarnations and are known to disturb sacrifices, desecrate graves and possess human beings. Translated to English, Rakshasa means injurer. They can shapeshift into anything, have superhuman strength and heightened senses. They cannot enter a home without an invitation and can be killed by a knife of pure brass.
A Rawhead is a type of boogeyman that lurks in basements and preys upon children. Rawheads are hairy, ragged-looking humanoids with leathery skin. Their hands and feet are clawed. They have superhuman strength and speed and their weakness is powerful electrocution.
Reapers are responsible for escorting deceased souls to the afterlife, and they refuse - or are unable - to tell the deceased what awaits them. Reapers serve Death and are not aligned with Heaven or Hell. Death may have created them, although this has yet to be clarified in canon. According to Castiel, reapers gather in groups "at times of great catastrophe" or distress, and he lists the Chicago Fire of 1871, the San Francisco Earthquake of 1906, and the destruction of Pompeii as examples. They are invisible to humans unless the person is near death or in spirit or astral projection form. They may also become visible to humans at will. They are able to stop time and are capable of altering human perception tomake themselves appear any way they want. They are vulnerable to Death's scythe, can be bound using spells and enochian runes, and can also be possessed by demons. It is unknown whether any demon can possess them or whether it must be a very powerful one. They can also be killed by an angel blade.
The rugaru is the result of a genetic mutation that, when expressed, causes the affected human to experience a murderous, cannibalistic hunger. Outwardly the rugaru can appear human for years, never knowing its true nature, but eventually it becomes consumed with a terrible hunger. During this time, it feeds on any meat it can get its hands on, until it finally gives in to the craving for human flesh. The rugaru will also demonstrate superhuman strength, and its bones will move under its skin. One bite of human flesh is all that's necessary for the rugaru to transform outwardly into a monster, at which point it can never appear or be human again. The only way to kill it is by setting it on fire, otherwise it will continue killing people to sate its hunger. It has enhanced physical atributes such as strength and speed and can only be killed by fire.
A pagan god that resides in an ancient tree brought to the US by Scandinavian immigrants. Each year the people of Burkitsville, Indiana present it with a young man and woman as a sacrifice to ensure the prosperity of their town and its crops. The god inhabits the form of a scarecrow made from the body of its previous victims and kills the couple with a hooked blade, or scythe. The god is vanquished when the sacred tree is destroyed with fire. This particular God's name is the Vanir.
(1) Supernatural Wiki