In the series, Demons are magical creatures renown for their cruelty and affiliation with dark magic. They are, for the most part, incredibly hard to defeat and can cause heavy damage and havoc if going on a rampage.
The Krylock Demon is a beast of pure evil that feeds on other magical creatures, such as Unicorns or Leprechauns. It has the head of a cobra and the body of a scorpion. Its venom is extremely dangerous since, if ingested, it can turn humans into Krylock-like creatures. Jake managed to defeat this Demon by turning its own stinger against it, planting it right through its chest.
The Shade Demons are creatures called forth from the shadows. They are the loyal servants and minions to the Dark Dragon. They have slender bodies and a skeletal appearance. Although they basically are made of shades, they can fight against others and cause physical harm. To defeat them, one must either deal strong blows to them or exploit their one weakness: light.
Since Shade Demons appear in both Seasons of the show, they have two different designs but still remain similar.
The Vault Demons are a trio of magical creatures so strong that they could not be destroyed. They had to be sealed away in the Fengdu Vault in order to be kept away from wrecking havoc across the land. These three Demons are extremely notorious and will not hesitate to attack anything or anyone on sight. Jake accidently lets them loose after handling the box they were sealed in upside down. He later manages to seal them back into the Fengdu Vault with the help of Fu Dog and his sister Haley.