There are dozens of different creatures/monsters/ghosts on this show. I listed as many as I thought were important, but it is a long list!! You might want to wait to go through this on a day when you are bored or need reasearch because of all of the content. Ok everyone, grab a Coke and a smile, because this is long!
Arachne are humanoid monsters with spider-like abilities and attributes. They haven't been seen outside of Crete in 2,000 years, but a female arachnid appears in Bristol, Rhode Island, in 2010/11. Their poisonous bite can turn humans into arachne. Once turned, arachne can mate and produce offspring. Because of their rarity, there is little lore on them or on how to kill them. Decapitation is the only sure way to kill it.(1)
Changelings are humanoid creatures with discolored, slimy skin, hollow eyes, and a round mouth with many teeth. They can appear human, but their true nature is revealed in their reflection. They feed on humans' synovial fluid. Their abilities include superior strength, sharp teeth for feeding on humans, and a lamprey-like mouth. They can appear human. Their weaknesses include fire, setting a changeling on fire will kill it, killing a mother changeling will cause it's children to die instantly and their true form is revealed in a mirror (1)
Croatoan is an illness described as a "blood-borne virus" that is demonic in origin, and causes a murderous rage in the people it infects. There is no cure for this virus, but the people infected can be killed by any normal means. It is passed by blood to blood contact.
Daevas are used by demons as invisible killers. They are considered a shadow demon, or demons of darkness. Because they are animalistic and savage in nature, even demons need special rituals to control them and they will turn on the demon if they regain control. They are Zoroastrian demons. They are invisible, have superhuman strength and possess claws. Their only weakness is extreme sunlight and that they cannot manifest without shadows.
Okamis are a humanoid monster. They hunt and feed on humans and usually develop a taste for a certain type of human. They are normally only found in Japan. They have superhuman strength and agility, possess fangs, and feed on humans. the only way they can be killed is by being stabbed seven times by a bamboo dagger that has been blessed by a Shinto priest, or, as Bobby finds out, a woodchipper.
!Death omens are apparitions of a deceased person or object. Usually, a death omen is an indicator tht the person who is visited by it is going to die. It can manifest in several places at once (bilocation), and to different people. Sometimes a death omen will try tocommnicate with the person they are appearing to, in order to warn them against impending danger.
(1) Supernatural Wiki