"Archfiend" is a special category of card introduced in the Dark Crisis expansion set. Most Archfiends can be identified by their name. Any card with "Archfiend" in the card name, is an Archfiend card. In addition, several older cards are also considered to be "Archfiends". These cards include:
Axe of Despair
B. Skull Dragon
Beast of Talwar
Fiend Skull Dragon
Lesser Fiend
Shadow Tamer
Summoned Skull
Toon Summoned Skull