Spiritual Beings
God is the Father, Son, and Holy Spirit. They are three persons but one in agreement and essence. God is the Creator. Go here.
Humans are designed in the image of God. Humans are three-fold beings. Humans are soul (mind, intellect, emotions, will), spirit body, and flesh body.
Go here.
Angels are servants of God. They have a mind, will, emotions, intellect, and a spirit body. Go here.
Demons are angels who followed Lucifer in a rebellion against God. The chief of the demons is Lucifer. These demons mask themselves to appear to be angels, ghosts, extra-terrestrial aliens, fairies, gods, goddesses, hybrid beings, and all other creatures mentioned in mythology. These demons constantly look for ways to deceive humans and detour humans from the true God. Go here. These demons influence such humans as occultists and those involved in religions other that Judaism and Christianity. Go here for more.
The animal and plant kingdoms encompass the only other creatures in existence. These creatures however are not spirit beings. They are only 'flesh' bodies that survive on genetically programmed functions.
There are no other beings nor creatures in existence.
--Jeremy Brown 2003
Addendum March 2023:
Among ancient Jewish and Christian writers that were not heretical, there is the belief that there was a second fall of angels who married women and had children. This is hinted at in Genesis. The fallen angels either took physical form and had sexual relations with the women to produce giant half breeds that were less than 15 feet tall. This may or may not have happened differently by the angels possessing the male and or female where giants wee produced in sexual relations. And so, some believe the deceased giants before and after the great flood were where demonc came from.