"... The Scriptures assert that there are Devils and Witches and that they are the common enemy of Mankind.
George Giffard, an Oxford preacher of about the same period, said that witches should be put to death not because they kill others but because they deal with devils: 'These cunning men and women which dealt with spirits and charm seeming to do good, and draw the people into manifold impieties, with all other which have familiarity with devils, or use conjurations, ought to be rooted out, that others might see and fear.' ..." Increase Mather, writing in Cases of Conscience (1693)
The ancient Celts had hundreds of Irish mythical deities, but as with most cultures, they had their demons. Some of the Celtic "monsters" were originally gods but were later demonized as pagan creatures when many of the Celts became Christians.