(This card is always treated as an "Archfiend" card.)The equipped monster gains 1000 ATK. When this card is sent from the field to the Graveyard: You can Tribute 1 monster; place this card on the top of your Deck.
Retrieving requires a tribute and prevents you from drawing a new card.
When Axe of Despair is sent to the graveyard, you can retrieve it by tributing Black Ptera on your field. Axe of Despair will return to the top of your deck, while Black Ptera would return to your hand. You could also use the tribute to remove undesirable monsters on your field like Lava Golem, or monsters who are useless on the field like ones affected by Floodgate Trap Hole.
Prior to that archetype condition being added to it, it had rulings stating it was an Archfiend card in the TCG. (Actually, they had a page dedicated to the Archfiends without Archfiend in their TCG name on the site, though they missed A Deal with Dark Ruler from it.)