Demons - A

Abaddon = The Angel of the Abyss, for more info see Abaddon.
Abaddon's Acolytes = These Fallen have pledged specific loyalty to the Archduke of Hell known as Abaddon (external link), the angel of the abyss and destroyer of the end times.  Abaddon demands that his followers be utterly ruthless and bloodthirsty, and that they must actively pursue the enemies of the Darkness.  But in return for such wanton devotion, Abaddon appraises his followers with powers similar to that of the Order of Destroyers.  Abbadon's Acolytes differ radically from other Infernalists in that they eschew the use of magick from a distance, instead they live to face their enemies in glorious hand-to-hand combat.  Much of their magick is used to bolster their physical attributes and imbue their weapons with dark power.
Addiction = Addiction is a weakness commonly exploited by the Darkness. See Addiction. 
Angel Hunter = Often Infernalists, these hunters lay traps and ambushes for members of the Angelic Hosts. For more info see Angel Hunter.
Anti Faith = The opposite of True Faith, Anti Faith represents a character's "faith in the Darkness." 
Antichrist = The future hope of demonkind on Earth, the Antichrist will usher in an age of Darkness. For more info see The Antichrist.
Apotheosis = Some Infernalists seek 'godhood' for themselves, although what exactly that means often changes with the individual. For most Infernalists, 'godhood' simply means attaining the same level of power and knowledge as the Pagan Gods. How they are supposed to attain this level of power usually involves building up sacrifices, stolen power and demonic favor. Some Infernalists believe they will be granted such power upon the End Times, when Hell will rule over Earth (the Lords of the Pit are really into this sort of thing). 
Army of Darkness = Legends tell of a massive army of feirce warriors, clad in armor forged from the souls of the lost. For more info see Army of Darkness. 
Asmodeus = An infamous Demon on Earth, the collector of people's secrets. For more info see Asmodeus.
Auguring = Auguring is an ancient practice of foretelling future events or outcomes by inspecting the entrails of a sacrifice (animal or otherwise). Infernalists often claim to gain insights into future events via auguring. 
Avatar of the Devil = A physical manifestation of a portion that is the being of Satan, also known as Lucifer. For more info see Avatar of the Devil.