A Dark Demon is technically any Demon which is covered with Darkness. Regular Demons are the most commonly encountered variety of Dark Demons, although any of the following may also be found in a 'Dark' variety: Crawler Demons, Cyber Demons, Dominator Demons, Hollow Demons, Masked Demons, Ninja Demons, Psychoram Demons and Punkgut Demons.
Dark Demons are generally more aggressive than their regular counterparts, and will attack Garcia head-on more frequently. The Darkness renders the Demons completely invincible, and they cannot be harmed until it is lifted. Using the Light Shot on a Dark Demon will remove the Darkness from its body, although this only works outside the Darkness. If the Demon enters the Darkness again, its body will become covered in Darkness once more. Garcia can also remove the Darkness by hitting a Demon with a simple torch-swing attack, but he cannot instant-kill them with a charged attack.
Some enemies will remain in their normal forms even when exposed to the Darkness, such as Mikami Heads, Darkness Hands and Blindness Hands. Hammerkop Demons are unique in that the Darkness will overload their bodies and kill them, releasing several regular Dark Demons from its corpse in the process.